JAVA PROGRAMJAVA PROGRJAVA PROGRJAVA.pptx

JAVA PROGRAM
SCION RESEARCH AND DEVELOPMENT

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language and why we use programming languages.
JAVA
Java Tutorial
It is one of the programming language or technology used for developing web
applications. Using this technology you can develop distributed application. A
Java language developed at SUN Micro Systems in the year 1995 under the
guidance of James Gosling and their team. In other word It is a programming
language suitable for the development of web applications. It is also used for
developing desktop and mobile application. Born
This language was developed at SUN Microsystems in the year 1995 under the
guidance of James Gosling and their team.
Prerequisites
Before learning of This tutorial no need to learn any programming
language like C and C++. But you have knowledge of programming

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Java is one of the programming language or technology used for developing web
applications. Java language developed at SUN Micro Systems in the year 1995
under the guidance of James Gosling and there team. Originally SUN Micro
Systems is one of the Academic university (Stanford University
Network)
JAV
A

JAVA
Whatever the software developed in the year 1990, SUN Micro Systems has
released on the name of oak, which is original name of java (scientifically oak is
one of the tree name). The OAK has taken 18 months to develop.
The oak is unable to fulfill all requirements of the industry. So James Gosling
again reviews this oak and released with the name of java in the year 1995.
Scientifically java is one of the coffee seed name.
Java divided into three categories, they are
J2SE (Java 2 Standard Edition)
J2EE (Java 2 Enterprise Edition)
J2ME (Java 2 Micro or Mobile Edition)
J2SE - J2SE is used for developing client side
applications.
J2EE - J2EE is used for developing server side
applications.
J2ME - J2ME is used for developing mobile or
wireless application.
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All versions of java
Java Version SE 7
J2SE 1.2 is called as
Dolphin and it is
released on 28 July,
2011.
Features
• Strings in switch
Statement
• Type Inference for Generic Instance
Creation, Multiple Exception Handling
• Support for Dynamic Languages
• Try with Resources
• Java nio Package
• Binary Literals, underscore in literals
• Diamond Syntax
• Automatic null Handling 5
JAVA VERSIONS

Java Version SE 6
J2SE 1.2 is called as Mustang and it is released on 11 December, 2006.
Features
• Scripting Language Support
• JDBC 4.0 API
• Java Compiler API
• Pluggable Annotations
• Native PKI, Java GSS, Kerberos and LDAP support.
• Integrated Web Services.
• Lot more enhancements.
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JAVA VERSIONS

J2SE Version 5.0
J2SE 1.2 is called as Tiger and it is released on 30 September, 2004.
Features
• Generics
• Enhanced for Loop
• Auto boxing/Unboxing
• Type safe Enums
• Varargs
• Static Import
• Metadata (Annotations)
• Instrumentation
JAVA VERSIONS
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J2SE Version 1.4
J2SE 1.2 is called as Merlin and it is released on 6 February, 2002.
Features
• XML Processing
• Java Print Service
• Logging API
• Java Web Start
• JDBC 3.0 API, Assertions
• Preferences API
• Chained Exception
• IPv6 Support
• Regular Expressions
JAVA VERSIONS
• Image I/O API
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J2SE Version 1.3
J2SE 1.2 is called as Kestrel and it is released on 8 May, 2000.
Features
• Java Sound
• Jar Indexing
• A huge list of enhancements in almost all the java area.
JAVA VERSIONS
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J2SE Version 1.2
J2SE 1.2 is called as playground and it is released on 8 December, 1998.
Features
• Collections framework.
• Java String memory map for constants.
• Just In Time (JIT) compiler.
• Jar Signer for signing Java Archive (JAR) files.
• Policy Tool for granting access to system resources.
• Java Foundation Classes (JFC) which consists of Swing 1.0, Drag and
Drop, and Java 2D class libraries.
• Java Plug-in
• Scrollable result sets, BLOB, CLOB, batch update, user-defined types in
JDBC.
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• Audio support in Applets.
JAVA VERSIONS

JDK Version 1.1
JDK 1.1 is released on 19 January, 1997
Features
• JDBC (Java Database connectivity)
• Inner Classes
• Java Beans
• RMI (Remote Method Invocation)
• Reflection(introspection only)
JDK Version 1.0
JDK 1.0 is called as OAK, and it is released on 23 January, 1996.
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JAVA VERSIONS

Basic Points of Java
Java is a platform independent, more powerful, secure, high
performance, multithreaded programming language. Here we discuss some
points related to Java.
Define byte
Byte code is the set of optimized instructions generated during
compilation phase and it is more powerful than ordinary pointer code.
Define JRE
The Java Runtime Environment (JRE)
is part of the Java
Development Kit(JDK). It contains a set of
libraries and tools for
developing Java application. The Java Runtime Environment
provides the
minimum requirements for executing a Java application
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JAVA BASIC

Define JVM
JVM is set of programs developed by sun Micro System and supplied as a part
of the JDK for reading line by line of byte code and it converts into a native
understanding form of operating system. The Java language is one of the
compiled and interpreted programming language.
Garbage Collector
The Garbage Collector is the system Java program which runs in the
background along with a regular Java program to collect un-Referenced
(unused) memory space for improving the performance of our applications.
Note: Java programming does not support destructor concept in place of
destructor, we have garbage collector program.
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JAVA BASIC

Define an API
An API (Application Programming Interface) is a collection of packages, a
package is the collection of classes, interfaces and sub-packages. A sub-
package is a collection of classes, Interfaces and sub packages etc.
Java programming contains user friendly syntax so that we can develop
effective applications. in other words if any language is providing user friendly
syntax, we can develop error free applications.
Definition of JIT
JIT is the set of programs developed by SUN Micro System and added as a
part of JVM, to speed up the interpretation phase.
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JAVA BASIC

Network based application
Network based application are mainly classified into two types.
1. Centralized Applications
2. Distributed Applications
Centralized
applications
• In this scenario multiple client
system depends on single server
system.
• The major drawback in this
architecture is if any problem
occurred on server system that will
be reflected on every client system.
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JAVA BASIC

Distributed applications
In this scenario multiple client system are depends on multiple server system
so that even problem occurred in one server will never be reflected on any
client system.
Note: In this architecture same
application is distributed in
multiple server system.
Java is a very powerful
language can be used to
developed both client server
architecture and distributed
architecture based application.
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JAVA BASIC

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• Simple
• Platform Independent
• Architectural Neutral
• Portable
• Multi Threading
• Distributed
• Networked
• Robust
• Dynamic
• Secured
• High Performance
• Interpreted
JAVA FEATURES
Features of Java
Features of a language are nothing but the set of services or facilities provided
by the language vendors to the industry programmers. Some important
features of java are;
Important Features of Java
• Object Oriented

Simple
It is simple because of the following factors:
• It is free from pointer due to this execution time of application is
improved. [Whenever we write a Java program without pointers then
internally it is converted into the equivalent pointer program].
• It has Rich set of API (application protocol interface).
• It has Garbage Collector which is always used to collect un-Referenced
(unused) Memory location for improving performance of a Java program. It
contains user friendly syntax for developing any applications.
JAVA FEATURES
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Platform Independent
A program or technology is said to be platform independent if and only if
which can run on all available operating systems with respect to its
development and compilation. (Platform represents O.S).
JAVA FEATURES
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Architectural Neutral
Architecture represents processor.
A Language or Technology is said to be Architectural neutral which can run on
any available processors in the real world without considering their
development and compilation.
JAVA FEATURES
The languages like C, CPP are treated as architectural dependent.
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Portable
If any language supports platform independent and architectural neutral
feature known as portable. The languages like C, CPP, Pascal are treated as non-
portable language. It is a portable language. According to SUN microsystem.
Multithreaded
A flow of control is known as a thread. When any Language executes
multiple thread at a time that language is known as multithreaded e. It is
multithreaded.
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JAVA FEATURES

Distributed
Using this language we can create distributed applications. RMI and EJB are
used for creating distributed applications. In distributed application multiple
client system depends on multiple server systems so that even problem
occurred in one server will never be reflected on any client system.
Note: In this architecture
same
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application is
distributed in multiple
server system.
JAVA FEATURES

Networked
It is mainly designed for web based applications, J2EE is used for
developing network based applications.
Robust
Simply means of Robust are strong. It is robust or strong Programming
Language because of its capability to handle Run-time Error, automatic garbage
collection, the lack of pointer concept, Exception Handling. All these points
make It robust Language.
Secure
It is a more secure language compared to other language; In this language,
all code is covered in byte code after compilation which is not readable by
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human.
JAVA FEATURES

Dynamic
It supports Dynamic memory allocation due to this memory wastage is reduce
and improve performance of the application. The process of allocating the
memory space to the input of the program at a run-time is known as dynamic
memory allocation, To programming to allocate memory space by dynamically
we use an operator called 'new' 'new' operator is known as dynamic memory
allocation operator.
Interpreted
It is one of the highly interpreted programming languages.
Object Oriented
It supports OOP's concepts because of this it is most secure language, for
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this topic you can read our oop's concepts in detail.
JAVA FEATURES

High performance
• It have high performance because of following reasons;
• This language uses Byte code which is faster than ordinary pointer code so
Performance of this language is high.
• Garbage collector, collect the unused memory space and improve the
performance of the application.
• It has no pointers so that using this language we can develop an
application very easily.
• It support multithreading, because of this time consuming process can be
reduced to executing the program.
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JAVA FEATURES

SET PATH
How to Set Path and Classpath in Java
Setting path and classpath in Java is very simple but before do this process you
need to know about path variable and classpath variable. Here I will show you
how to set path and classpath in Java in very simple and easy way.
Path Variable
Path variable is set for providing path for all Java tools like java, javac, javap,
javah, jar, applet viewer which are used in java programming. All these tools are
available in bin folders so we set path up to bin folders.
Classpath Variable
Classpath variable is set for providing a path for predefined Java classes
which is used in our application. All classes are available in lib/rt.jar so we
set classpath upto lib/rt.jar.
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SET PATH
JDK Folder Hierarchy
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Why set path ?
The following programming error is generally for all Java programmers when
they compile any Java program.
'javac' is not recognized as an internal or external command, operable
program or batch file.
When you get this type of error, then your operating system cannot find the
Java compiler (javac). To solve this error you need to set the PATH variable.
Javac is a tool which is available in bin folder so you must set the PATH upto
bin folder. In a bin folder all tools are available like javap, javah, jar, javac,
java, appletviewer etc. All these tools are used for different- different purpose.
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SET PATH

SET PATH
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set the path and classpath
Go on my computer icon and right click, after that click on properties
option.
SET PATH
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SET PATH
Now click on advance setting
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Click on advance Click on Environment variables
SET PATH
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Now one dialog box is appear,
now ignore this but do not close.
SET PATH
Click on new button which is below the first box.
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SET PATH
Now open my computer open c:/ > Programs Files > java > java1.6.0 > bin
copy this path
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SET PATH
Now come back on previous open dilogbox and write variable name 'path' and
for variable value paste all copied path up to the bin folder. Put .; at the end. It
(.) selects all the tools from the bin folder.
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Now open my computer open c:/ > Programs Files > java > java1.6.0 > jre >
lib > rt.jar copy this path
Note: rt.jar is available in lib folder this jar files contains all classes of jdk.
SET PATH
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Note: Finally after set classpath
Restart your system, or you can re-
open command prompt. 37
SET PATH
Now again come back on Environment variable dilogbox and click on new. Now
one box is open and write path variable as 'classpath' and for variable value
paste all copied paths upto rt.jar. Put .; at the end. It (.) selects all the classes
from lib folder.

Path classpath
path variable is set for providing path for all
java tools like java, javac, javap, javah, jar,
appletviewer
classpath variable is set for provide path of all
java classes which is used in our application.
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SET PATH
Difference between path and classpath in Java
• Path - Path variable is set for providing path for all Java tools like java,
javac, javap, javah, jar, appletviewer. In Java to run any program we use java
tool and for compile Java code use javac tool. All these tools are available in
bin folder so we set path upto bin folder.
• Classpath - classpath variable is set for providing path of all Java classes
which is used in our application. All classes are available in lib/rt.jar so we
set classpath upto lib/rt.jar.

SET PATH
JDK Folder Hierarchy
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All the tools are present in bin folder so we set path upto bin folder.
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SET PATH
Path variable is set for use all the tools like java, javac, javap, javah, jar,
appletviewer etc.
Example
"C:Program FilesJavajdk1.6.0bin"

SET PATH
Classpath variable is used to set the path for all classes which is used in our
program so we set classpath upto rj.jar. in rt.jar file all the .class files are
present. When we decompressed rt.jar file we get all .class files.
Example
"C:Program FilesJavajre1.6.0jrelibrt.jar" In above rt.jar is a jar file
where all the .class files are present so we set the classpath upto rt.jar.
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FIRST JAVA PROGRAM
First Java Program
Requirements for java Program
For executing any java program we
need given things.
• Install the JDK any version if
you don't have installed it.
• Set path of the jdk/bin directory.
• Create the java program
• Compile and run the java
program
Steps For compiling and
executing the java program
• Java is very simple programming language first we write a java program and
save it with program class name.
• In below program we create a java program with "First" name so we
save this program with "First.java" file name. We can save our java
program anywhere in our system or computer.
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Create First program
Example
class First{
public static void main(String[] args)
{
System.out.println("Hello Java");
System.out.println("My First Java Program");
} }
Compile and Execute Java Code
To compile: javac First.java
To execute: java First
Output
Hello Java
FIRST JAVA PROGRAM
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My First Java Program

Save Java Program
Syntax: Filename.java
Example: First.java
Compile Java Program
Syntax: Javac
Filename.java
Example: Javac First.java
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Note: Here Javac and Java are called tools or application programs or exe files
developed by sun micro system and supply as a part of jdk 1.5/1.6/1.7 in bin
folder. Javac is used for compile the java program and java is used for run the
java program.
FIRST JAVA PROGRAM

FIRST JAVA PROGRAM
During the program execution internally following steps will be
occurs.
• Class loader subsystem loads or transfer the specified class into main
memory(RAM) from secondary memory(hard disk)
• JVM takes the loaded class
• JVM looks for main method because each and every java program start
executing from main() method.
• Since main() method of java is static in nature, JVM call the main() method
with respect to loaded class (Example: First as First.main(--))
• Note: A java program can contain any number of main method but JVM start
execution from that main() method which is taking array of object of
String class.
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The java launcher tool then runs your application with an instance of the
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Java Virtual Machine (JVM).
FIRST JAVA PROGRAM
Compile and Run Java Program
In the Java programming language, all source code is first written in plain text
files and save with the .java extension. After compilation, .class files are
generated by javac compiler. A .class file does not contain code that is native to
your processor; it instead contains bytecodes (it is machine language of the
Java Virtual Machine1 (JVM)).

FIRST JAVA PROGRAM
Steps For compile Java Program
First Save Java program with same as
class name with .java extension.
Example: Sum.java
Compile: javac Filename.java
Example: javac Sum.java
Note: Here javac is tools or application
programs or exe files which is used for
Compile the Java program.
Steps For Run Java Program - For run java program use java tool.
Run by: java Filename , Example: java sum
Note: Here java is tools or application programs or exe files which is used
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for run the Java program.

FIRST JAVA PROGRAM
Steps For compiling and executing the java program
The following sequence of steps represented in the diagram use compiling the
java program and executing the java programs.
In the above diagram javac and
java are called tools or
application programs or exe
files developed by sun micro
system and supply as a part of
jdk 1.5/1.6/1.7 in bin folder
(starting directory of java is
called java home directory).
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DIFFERENCE B/W JDK,JVM, & JRE
Difference between JDK, JVM and JRE
JVM, JRE, JDK these all the backbone of java language. Each components have
separate works. JDK and JRE physically exists but JVM are abstract machine it
means it not physically exists.
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JVM
JVM (Java Virtual Machine) is a software. It is a specification that provides
runtime environment in which java bytecode can be executed. It not physically
exists. JVMs are not same for all hardware and software, for example for
window os JVM is different and for Linux VJM is different. JVM, JRE and JDK
are platform dependent because configuration of each OS differs. But, Java is
platform independent.
JRE
The Java Runtime Environment (JRE) is part of the Java Development Kit
(JDK). It contains set of libraries and tools for developing java application.
The Java Runtime Environment provides the minimum requirements for
executing a Java application. It physically exists. It contains set of libraries +
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other files that JVM uses at runtime.

JDK
The Java Development Kit (JDK) is primary components. It physically exists.
It is collection of programming tools and JRE, JVM.
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JVM ARCHITECTURE
JVM Architecture in Java
JVM (Java Virtual Machine) is a software. It is a specification that provides
Runtime environment in which java bytecode can be executed.
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Operation of JVM
JVM mainly performs following operations.
• Allocating sufficient memory space for the class properties.
• Provides runtime environment in which java byte code can be executed
• Converting byte code instruction into machine level instruction.
• JVM is separately available for every Operating System while installing java
software so that JVM is platform dependent.
Note: Java is platform Independent but JVM is platform dependent because
every Operating system have different-different JVM which is install along with
JDK Software.
Class loader subsystem:
Class loader subsystem will load the .class file into java stack and later
sufficient memory will be allocated for all the properties of the java
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program into following five memory locations.
JVM ARCHITECTURE

• Heap area
• Method area
• Java stack
• PC register
• Native stack
Heap area: - In which object references will be stored.
Method area - In which static variables non-static and static method will be
stored.
Java Stack - In which all the non-static variable of class will be stored and
whose address referred by object reference.
Pc Register
Which holds the address of next executable instruction that means that use
the priority for the method in the execution process?
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JVM ARCHITECTURE

Native Stack
Native stack holds the instruction of native code (other than java code) native
stack depends on native library. Native interface will access interface between
native stack and native library.
Execution Engine
Which contains Interpreter and JIT compiler whenever any java program is
executing at the first time interpreter will comes into picture and it converts
one by one byte code instruction into machine level instruction JIT compiler
(just in time compiler) will comes into picture from the second time onward if
the same java program is executing and it gives the machine level instruction to
the process which are available in the buffer memory.
Note: The main aim of JIT compiler is to speed up the execution of java
program.
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JVM ARCHITECTURE

JVM ARCHITECTURE
What is JIT and Why use JIT
• JIT is the set of programs developed by SUN Micro System and added as a
part of JVM, to speed up the interpretation phase.
• In the older version of java compilation phase is so faster than
interpretation phase. Industry has complained to the SUN Micro System
saying that compilation phase is very faster and interpretation phase is very
slow.
• So solve this issue, SUN Micro System has developed a program called JIT
(just in time compiler) and added as a part of JVM to speed up the
interpretation phase. In the current version of java interpretation phase is
so faster than compilation phase. Hence java is one of the highly
interpreted programming languages.
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Object and class in Java
Object is the physical as well as logical entity where as class is the only logical
entity.
Class: Class is a blue print which is containing only list of variables and
method and no memory is allocated for them. A class is a group of objects
that has common properties.
A class in java contains:
• Data Member
• Method
• Constructor
• Block
• Class and Interface 57
OOPS CONCEPT

OOPS CONCEPT
Object: Object is a instance of class, object has state and behaviors.
An Object in java has three characteristics:
• State
• Behavior
• Identity
State: Represents data (value) of an object.
Behavior: Represents the behavior (functionality) of an object such as deposit,
withdraw etc.
Identity: Object identity is typically implemented via a unique ID. The value of
the ID is not visible to the external user. But, it is used internally by
the JVM to identify each object uniquely.
Class is also can be used to achieve user defined data types.
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OOPS CONCEPT
Real life example of object and class
In real world many examples of object and class like dog, cat, and cow are
belong to animal's class. Each object has state and behaviors.
For example a dog has state:- color, name, height, age as well as
behaviors:- barking, eating, and sleeping.
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Vehicle class
Car, bike, truck these all are belongs to vehicle class. These Objects have also
different states and behaviors.
For Example car has state - color, name, model, speed, Mileage. as we;; as
behaviors - distance travel
OOPS CONCEPT
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Class Object
1
Class is a container which
collection of variables and
methods.
object is a instance of class
2
No memory is allocated at the
time of declaration
Sufficient memory space will be
allocated for all the variables of class
at the time of declaration.
3
One class definition should exist
only once in the program.
For one class multiple objects can be
created.
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method; }
Syntax to declare a Class
class Class_Name {
data member;
OOPS CONCEPT
Difference between Class and Object in Java

OOPS CONCEPT
Simple Example of Object and Class
In this example, we have created a Employee class that have two data members
eid and ename. We are creating the object of the Employee class by new
keyword and printing the objects value.
package sample;
public class Program1 {
int eid; // data member (or instance variable) String
ename; // data member (or instance variable)
{
eid=101;
ename="Hitesh";
}
public static
void main(String
args[]){
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Program1 e=new Program1();

OOPS CONCEPT
// Creating an object of class Employee
System.out.println("Employee ID: "+e.eid);
System.out.println("Name: "+e.ename);
}
}
OUTPUT:
Employee ID: 101
Name: Hitesh
Note: A new keyword is used to allocate memory at runtime, new keyword is
used for create an object of class, later we discuss all the way for create an
object of class.
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Data Type in Java
Data type is a special keyword used to allocate sufficient memory space for
the data, in other words Data type is used for representing the data in main
memory (RAM) of the computer.
In general every programming language is containing three categories of
data types. They are
• Fundamental or primitive data types
• Derived data types
• User defined data types.
DATA TYPE IN JAVA
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Primitive data types
• Primitive data types are those whose variables allows us to store only one
value but they never allows us to store multiple values of same type.
• This is a data type whose variable can hold maximum one value at a
time.
Example
int a; // valid
a=10; // valid
a=10, 20, 30; //
invalid
Here "a" store
only one value
at a time
because it is
primitive type
variable.
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DATA TYPE IN JAVA

Derived data types
• Derived data types are those whose variables allow us to store multiple
values of same type. But they never allows to store multiple values of
different types.
• These are the data type whose variable can hold more than one value of
similar type. In general derived data type can be achieve using array.
Example
int a[] = {10,20,30}; // valid
int b[] = {100, 'A', "ABC"}; // invalid
Here derived data type store only same type of data at a time not store integer,
character and string at same time.
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DATA TYPE IN JAVA

User defined data types
• User defined data types are those which are developed by programmers by
making use of appropriate features of the language.
• User defined data types related variables allows us to store multiple
values either of same type or different type or both. This is a data type
whose variable can hold more than one value of dissimilar type, in java it is
achieved using class concept.
Note: In java both derived and user defined data type combined name as
reference data type.
In C language, user defined data types can be developed by using struct,
union, enum etc. In java programming user defined datatype can be
developed by using the features of classes and interfaces.
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DATA TYPE IN JAVA

Example
Student s = new Student(); In java we have eight data type which are
organized in four groups. They are
Integer category data types
Character category data types
Float category data types
Boolean category data types
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DATA TYPE IN JAVA

Integer category data types
These category data types are used for storing integer data in the main
memory of computer by allocating sufficient amount of memory space.
Integer category data types are divided into four types which are given in
following table Data Type Size Range
1 Byte 1 + 127 to -128
2 Short 2 + 32767 to -32768
3 Int 4 + x to - (x+1)
4 Long 8 + y to - (y+1)
Character category data types
A character is an identifier which is enclosed within single quotes. In java to
represent character data, we use a data type called char. This data type takes
two byte since it follows Unicode character set.
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Data Type Size(Byte) Range
Char 2 232767 to -32768
DATA TYPE IN JAVA

Data Type Size Range Number of decimal places
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Float 4 +2147483647 to -2147483648 8
Double 8 + 9.223*1018 16
DATA TYPE IN JAVA
Why Java take 2 byte of memory for store character ?
Java support more than 18 international languages so java take 2 byte for
characters, because for 18 international language 1 byte of memory is not
sufficient for storing all characters and symbols present in 18 languages. Java
supports Unicode but c support ascii code. In ascii code only English language
are present, so for storing all English latter and symbols 1 byte is sufficient.
Unicode character set is one which contains all the characters which are
available in 18 international languages and it contains 65536 characters
Float category data types
Float category data type are used for representing float values. This category
contains two data types, they are in the given table

Boolean category data types
Boolean category data type is used for representing or storing logical values is
true or false. In java programming to represent Boolean values or logical values,
we use a data type called Boolean.
Why Boolean data types take zero byte of memory ?
Boolean data type takes zero bytes of main memory space because Boolean
data type of java implemented by Sun Micro System with a concept of flip -
flop. A flip - flop is a general purpose register which stores one bit of
information (one true and zero false).
Note: In C, C++ (Turbo) Boolean data type is not available for representing true
false values but a true value can be treated as non-zero value and false
values can be represented by zero
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DATA TYPE IN JAVA

Data Type Default Value Default size
boolean False 1 bit
char 'u0000' 2 byte
byte 0 1 byte
short 0 2 byte
int 0 4 byte
long 0L 8 byte
float 0.0f 4 byte
double 0.0d 8 byte
72
DATA TYPE IN JAVA

Syntax
Variable_name = value;
73
VARIABLE DECLARATION IN JAVA
Variable Declaration Rules in Java
Variable is an identifier which holds data or another one variable is an
identifier whose value can be changed at the execution time of program.
Variable is an identifier which can be used to identify input data in a program.

Rules to declare a Variable
• Every variable name should start with either alphabets or underscore ( _ ) or
dollar ( $ ) symbol.
• No space are allowed in the variable declarations.
• Except underscore ( _ ) no special symbol are allowed in the middle of
variable declaration
• Variable name always should exist in the left hand side of assignment
operators.
• Maximum length of variable is 64 characters.
• No keywords should access variable name.
Note: Actually a variable also can start with ¥,¢, or any other currency sign.
74

Example of Variable Declaration
class Sum
{
{
int _a, ¢b, ¥c, $d, result;
_a=10;
¢b=20;
¥c=30;
$d=40; result=_a+
¢b+¥c+$d;
System.out.println("S
um is :" +result);
}
Output
Sum is : 100
75
}

Variable initialization
It is the process of storing user defined values at the time of allocation of
memory space.
Variable declarations
In which sufficient memory will be allocated and holds default values.
Syntax
Datatype variable_name;
byte b1;
76

Syntax
int a= 100;
int b;
b = 25; //
------>
direct
assigned
variable
b = a; //
------>
Variable assignment
Value is assigned to a variable if that is already declared or initialized.
Syntax
Variable_Name = value
int a = 100;
77

Operators in Java
Operator is a special symbol that tells the compiler to perform specific
mathematical or logical Operation. Java supports following lists of operators.
• Arithmetic Operators
• Relational Operators
• Logical Operators
• Bitwise Operators
• Assignment Operators
• Ternary or Conditional Operators
OPERATORS IN JAVA
78

Arithmetic Operators
Given table shows all the
and B hold 3.
79
Arithmetic
supported
Language.
operator
by Java
Lets suppose
Operator Example (int A=8, B=3) Result
+ A+B 11
- A-B 5
* A*B 24
/ A/B 2
% A%4 0
variable A hold 8 and B
hold 3.
Relational Operators
Which can be used to check
the Condition, it always
return true or false. Lets
suppose variable A hold 8
Operators Example (int A=8, B=3) Result
< A<B False
<= A<=10 True
> A>B True
>= A<=B False
== A== B False
!= A!=(-4) True
OPERATORS IN JAVA

Logical Operator
Which can be used to combine more than one Condition?. Suppose you want to
combined two conditions A<B and B>C, then you need to use Logical
Operator like (A<B) && (B>C). Here && is Logical Operator
80
Truth table of Logical Operator
Operator Example (int A=8, B=3, C=-10) Result
&& (A<B) && (B>C) False
|| (B!=-C) || (A==B) True
! !(B<=-A) True
C1 C2 C1 && C2 C1 || C2 !C1 !C2
T T T T F F
T F F T F T
F T F T T F
F F F F T T
OPERATORS IN JAVA

Assignment operators
Which can be used to assign a value to a variable. Lets suppose variable A
hold 8 and B hold 3.
81
Operator Example (int A=8, B=3) Result
+= A+=B or A=A+B 11
-= A-=3 or A=A+3 5
*= A*=7 or A=A*7 56
/= A/=B or A=A/B 2
%= A%=5 or A=A%5 3
=a=b Value of b will be assigned to a
Ternary operator
If any operator is used on three operands or variable is known as ternary
operator. It can be represented with " ?: "
OPERATORS IN JAVA

STRUCTURE OF JAVA PROGRAM
Structure of Java Program
• Structure of a java program is the standard format released by Language
developer to the Industry programmer.
• Sun Micro System has prescribed the following structure for the java
programmers for developing java application.
82

• A package is a collection of classes, interfaces and sub-packages. A sub
package contains collection of classes, interfaces and sub-sub packages etc.
java.lang.*; package is imported by default and this package is known as default
package.
• Class is keyword used for developing user defined data type and every java
program must start with a concept of class.
"ClassName" represent a java valid variable name treated as a name of the
class each and every class name in java is treated as user-defined data type.
• Data member represents either instance or static they will be selected based
on the name of the class.
• User-defined methods represents either instance or static they are meant
for performing the operations either once or each and every time.
• Each and every java program starts execution from the main() method. And
83
hence main() method is known as program driver.

• Since main() method of java is not returning any value and hence its return
type must be void.
• Since main() method of java executes only once throughout the java program
execution and hence its nature must be static.
• Since main() method must be accessed by every java programmer and
hence whose access specifies must be public.
•Each and every main() method of java must take array of objects of String.
Block of statements represents set of executable statements which are in
term calling user-defined methods are containing business-logic.
The file naming conversion in the java programming is that which-ever class is
containing main() method, that class name must be given as a file
name with an extension .java.
84

MAIN() METHOD IN JAVA
Main() Method in Java
main() method is starting execution block of a java program or any java
program start their execution from main method. If any class contain main()
method known as main class.
Syntax of main() method:
Syntax
public static void main(String args[])
{
.......
.......
}
85

Public
public is a keyword in a java language whenever if it is preceded by main()
method the scope is available anywhere in the java environment that means
main() method can be executed from anywhere. main() method must be
accessed by every java programmer and hence whose access specifier must be
public.
Static
static is a keyword in java if it is preceded by any class properties for that
memory is allocated only once in the program. Static method are executed only
once in the program. main() method of java executes only once throughout the
java program execution and hence it declare must be static.
86

Void
void is a special data type also known as no return type, whenever it is
preceded by main() method that will be never return any value to the
operating system. main() method of java is not returning any value and hence
its return type must be void.
String args[]
String args[] is a String array used to hold command line arguments in the
form of String values.
In case of main() method following changes are acceptable
1. We can declare String[] in any valid form.
• String[] args
• String args[]
• String []args
87

2. Instance of String[] we can take var-arg String parameter is String...
Syntax
main(String[] args) --> main(String... args)
3.We can change the order of modifiers i.e Instead of
Syntax
public static we can take static public
4. Instead of args we can take any valid java identifier.
Syntax
public static void main(String a[])
88

89
Example of override main() method
public class mainclass
{
{
System.out.println("Execution starts from
Main()");
}
void main(int args)
System.out.println("Override main()");
}
double main(int i, double d)
{
System.out.println("Override main()");
return d;
}
}
Output
Execution starts from Main()
We can overload main() method ?
Yes, We can overload main() method. A Java class can have any number of
main() methods. But run the java program, which class should have main()
method with signature as "public static void main(String[] args). If you do any
modification to this signature, compilation will be successful. But, not run the
java program. we will get the run time error as main method not found.

COMMAND LINE
Command Line Arguments in Java
If any input value is passed through the command prompt at the time of
running of the program is known as command line argument by default
every command line argument will be treated as string value and those are
stored in a string array of main() method.
Syntax for Compile and Run CMD programs
Compile By -> Javac Mainclass.java
Run By -> Java Mainclass value1 value2 value3 ....................
90

COMMAND LINE
Program Command Line Argument in Java
class CommandLineExample
{
{
System.out.println("Argument is: "+args[0]);
}
}
Compile and Run above programs
Compile By > Javac CommandLineExample.java
Run By > Java CommandLineExample Porter
Output
Argument is: Porter
91

COMMAND LINE
Example of command-line argument in java
class SumDemo
{
{
System.out.println("Sum: "+args[0]);
}
}
Compile and Run above programs
Compile By > Javac SumDemo.java
Run By > Java SumDemo
10 20
Output
92
Sum: 30

COMMAND LINE
• When the above statement is executing the following sequence of steps will
take place.
• Class loader sub-system loads SumDemo along with Command line
argument(10, 20) and in main memory.
• JVM takes the loaded class SumDemo along
• with Command line arguments (10, 20) and place the number of values in
the length variable that is 2.
• JVM looks for main() that is JVM will place the Command in the main() in
the form of string class that is.
• Hence all the CMD line arguments of Java are sending to main() method
available in the form of an array of object of String class (every CMD are
available or stored in main method in the form of an array of object of
String class). JVM calls the main() method with respect to load class
93
SumDemo that is SumDemo.main().

Accept command line arguments and display their values
class CMD
{
public static void main(String k[])
{
System.out.println("no. of arguments ="+k.length);
for(int i=0;i< k.length;i++)
{
System.out.println(k[i]);
}
}
}
Note: Except + operator
any numeric
operation
not allowed in command
line arguments.
94
COMMAND LINE

class squareDemo
{ int no, result;
void square(String
s) {
int no=Integer.parseInt(s);
result=no*no;
System.out.println("Square: " +result);
} }
class CMD {
{ System.out.println("no of arguments:
"+args.length);
squareDemo obj=new squareDemo();
obj.square(args[0]);
} }
95
COMMAND LINE
Square of Number by reading value from command prompt.

System.out.println() in Java
In java language print() and println() are the predefined non-static method
of printStream class used to display value or message either in the same line or
line by line respectively. PrintStream class is having fixed object reference in the
System class (existing as a static properties) so that either print() or println()
method can be called with following syntax..
PRINT LINE
96

Syntax
System.out.print("--------------");
System.out.println("------------");
/* "out" is Object reference of printStream class existing in system class as
a static property. */
97
Example
class PrintStream {
println() { //-----------> non-static
........
}
//-----------> non-static
print() {
........
} }
class System
{
Static PrintStream out;
Static PrintStream err;
}
PRINT LINE

Examples of SOP Statements
Example
System.out.println("Hello"); // ---------> Hello
int x=10, y=20;
System.out.println("x");
System.out.println(x);
// ---------> x
// ---------> 10
System.out.println("Hello"+x);
System.out.println(x+y);
System.out.println(x+y+"Hello");
// ---------> Hello10
// ---------> 30
// ---------> 1020Hello
Example
class Hello {
public static void main(String arg[]) {
System.out.println("Hello word");
Output
Hello Word
PRINT LINE
98
} }

DECISION MAKING STMT
Decision Making Statement in Java
Decision making statement statements is also called selection statement.
That is depending on the condition block need to be executed or not which is
decided by condition. If the condition is "true" statement block will be
executed, if condition is "false" then statement block will not be executed. In
java there are three types of decision making statement.
• if
• if-else
• switch
if-then Statement
if-then is most basic statement of Decision making
statement. It tells to program to execute a certain part
of code only if particular condition is true. 99

Syntax
if(condition)
{
Statement(s)
}
Example if statement
class Hello {
int a=10;
{ if(a<15) {
System.out.println("Hello good
morning!");
Hello good morning
100
}
}
}
Output

if-else statement
In general it can be used to execute one block of statement among two blocks,
in java language if and else are the keyword in java.
Syntax
if(condition)
{
Statement(s)
}
else
{
Statement(s)
}…
101

In the above syntax whenever condition is true all the if block statement are
executed, remaining statement of the program by neglecting. If the condition is
false else block statement executed and neglecting if block
statements.
102

Example if else
import java.util.Scanner;
class Oddeven {
public static void
main(String[] args){
int no;
Scanner s=new Scanner(System.in);
System.out.println("Enter any number :");
no=s.nextInt();
if(no%2==0)
{ System.out.println("Even
number");
}
else {
System.out.println("Odd number");
Output
Enter any number :
10
Even number
103
} } }

Switch Statement
The switch statement in java language is used to execute the code from
multiple conditions or case. It is same like if else-if ladder statement.
A switch statement work with byte, short, char and int primitive data type,
it also works with enumerated types and string.
Syntax
switch(expression/variable)
{ case value:
//statements
// any number of case statements
break; //optional
default: //optional
//statements
104
}
SWITCH STATEMENT

Rules for apply switch statement
With switch statement use only byte, short, int, char data type (float data type
is not allowed). You can use any number of case statements within a switch.
Value for a case must be same as the variable in switch.
Limitations of switch statement
Logical operators cannot be used with switch statement. For instance
Example
SWITCH STATEMENT
105
case k>=20: // not allowed

Example of switch case
import java.util.*;
class switchCase {
public static void
main(String
arg[]) {
int ch;
System.out.println("Enter any number (1 to 7) :");
Scanner s=new Scanner(System.in); ch=s.nextInt();
switch(ch) {
case 1: System.out.println("Today is Monday");
break;
case 2: System.out.println("Today is Tuesday");
break;
106
SWITCH STATEMENT

Output
Enter any number (1 to 7) :
5
SWITCH STATEMENT
case 3: System.out.println("Today is Wednesday");
break;
case 4: System.out.println("Today is Thursday");
break;
case 5: System.out.println("Today is Friday");
break;
case 6: System.out.println("Today is Saturday");
break;
case 7: System.out.println("Today is Sunday"); default:
System.out.println("Only enter value 1 to 7");
} } }
Today is Friday 107

LOOPING STATEMENT
Looping Statement in Java
Looping statement are the statements execute one or more statement
repeatedly several number of times. In java programming language there are
three types of loops; while, for and do-while.
Why use loop ?
When you need to execute a block of code several number of times then you
need to use looping concept in Java language.
Advantage with looping statement
• Reduce length of Code
• Take less memory space.
• Burden on the developer is reducing.
• Time consuming process to execute the program is reduced.
108

LOOPING STATEMENT
Difference between conditional and looping statement
Conditional statement executes only once in the program where as looping
statements executes repeatedly several number of time.
While loop
In while loop first check the condition if condition is true then control goes
inside the loop body otherwise goes outside of the body. while loop will be
repeats in clock wise direction
Syntax
while(condition)
{
Statement(s)
Increment / decrements (++ or --);
} 109

Example while loop
class whileDemo {
{ int i=0;
while(i<5)
{ System.out.println(+i
); i++;
}
Output
0
1
2
3
LOOPING STATEMENT
4 110

for loop
for loop is a statement which allows code to be repeatedly executed. For
loop contains 3 parts Initialization, Condition and Increment or
Decrements
Syntax
for ( initialization; condition; increment )
{
statement(s);
}
LOOPING STATEMENT
111

• Initialization: This step is execute first and this is execute only once when
we are entering into the loop first time. This step is allow to declare and
initialize any loop control variables.
• Condition: This is next step after initialization step, if it is true, the body of
the loop is executed, if it is false then the body of the loop does not execute
and flow of control goes outside of the for loop.
• Increment or Decrements: After completion of Initialization and
Condition steps loop body code is executed and then Increment or
Decrements steps is execute. This statement allows to update any loop
LOOPING STATEMENT
112
control variables.

Control flow of for loop
• First initialize the variable
• In second step check condition
• In third step control goes inside loop body and execute.
• At last increase the value of variable
113
• Same process is repeat until condition not false.
LOOPING STATEMENT

LOOPING STATEMENT
Display any message exactly 5 times.
Example of for loop
class Hello {
public static void main(String args[]) {
int i;
for (i=0; i<5; i++)
{ System.out.println("Hello
Friends !");
} } }
Output
Hello Friends !
Hello Friends !
Hello Friends !
Hello Friends ! 114
Hello Friends !

do-while
• A do-while loop is similar to a while loop, except that a do-while loop is
execute at least one time.
• A do while loop is a control flow statement that executes a block of code at
least once, and then repeatedly executes the block, or not, depending on a
given condition at the end of the block (in while).
Syntax
do
{
Statement(s)
increment/decrement (++ or --)
}
115
while();
LOOPING STATEMENT

LOOPING STATEMENT
When use do..while loop
• when we need to repeat the statement block at least one time then use do-
while loop. In do-while loop post-checking process will be occur, that is after
execution of the statement block condition part will be executed.
• In below example you can see in this program i=20 and we check condition i
is less than 10, that means condition is false but do..while loop execute once
and print Hello world ! at one time.
116

Example do..while loop
class dowhileDemo {
{ int i=20;
do {
System.out.println("Hello world !");
i++;
}
while(i<10);
}
}
Output
LOOPING STATEMENT
117
Hello world !

118
Example do..while loop
class dowhileDemo {
{ int i=0;
do
{ System.out.println(+i
); i++;
}
while(i<5);
} }
Output
1
2
3
4
LOOPING STATEMENT
5

Wrapper classes in java
For each and every fundamental data type there exist a pre-defined class, Such
predefined class is known as wrapper class. The purpose of wrapper class is to
convert numeric string data into numerical or fundamental data. Why use
wrapper classes ?
We know that in java whenever we get input form user, it is in the form of
string value so here we need to convert these string values in different datatype
(numerical or fundamental data), for this conversion we use wrapper classes.
119
WRAPPER CLASS

}
Output
Sum before: 1020
WRAPPER CLASS
Example of wrapper class
class WraperDemo {
{ String s[] = {"10", "20"};
System.out.println("Sum before:"+ s[0] + s[1]); // 1020 int
x=Integer.parseInt(s[0]); // convert String to Integer int
y=Integer.parseInt(s[1]); // convert String to Integer int
z=x+y;
System.out.println("sum after: "+z); // 30
}
Sum after: 30 120

WRAPPER CLASS
Explanation: In the above example 10 and 20 are store in String array and next
we convert these values in Integer using "int x=Integer.parseInt(s[0]);" and "int
y=Integer.parseInt(s[1]);" statement In "System.out.println("Sum before:"+ s[0]
+ s[1]);" Statement normally add two string and output is 1020 because these
are String numeric type not number.
121

Converting String data into fundamental or numerical
We know that every command line argument of java program is available in
the main() method in the form of array of object of string class on String data,
one can not perform numerical operation. To perform numerical operation it
is highly desirable to convert numeric String into fundamental numeric value.
Example
• "10" --> numeric String --> only numeric string convert into numeric
type or value.
• "10x" --> alpha-numeric type --> this is not conversion.
• "ABC" --> non-numeric String no conversion.
• "
A" --> char String no conversion.
Only '
A'is convert into ASCII value that is 65 but '
A'is not convert into numeric
value because it is a String value.
122
WRAPPER CLASS

Fundamental DataType Wrapper CalssName
Conversion method from numeric string into
fundamental or numeric value
Byte Byte public static byte parseByte(String)
Short Short public static short parseShort(String)
Int Integer public static integer parseInt(String)
Long Long public static long parseLong(String)
float Float public static float parseFloat(String)
double Double public static double parseDouble(String)
char Character
boolean Boolean public static boolean parseBoolean(String)
123
WRAPPER CLASS
Fundamental data type and corresponding wrapper classes
The following table gives fundamental data type corresponding wrapper class
name and conversion method from numerical String into numerical values or
fundamental value.

WRAPPER CLASS
How to use wrapper class methods
All the wrapper class methods are static in nature so we need to call these
method using class.methodName().
• for Integer: int x=Integer.parseInt(String);
• for float: float x=Float.parseFloat(String);
• for double: double x=Double.parseDouble(String);
Each and every wrapper class contains the following generalized method for
converting numeric String into fundamental values.
124
Here xxx represents any fundamental data type.

NAMING CONVERSION
Naming Conversion of Java
Sun micro system was given following conversions by declaring class,
variable, method etc. So that it is highly recommended to follow this conversion
while writing real time code.
Why Using naming Conversion
Different Java programmers can have different styles and approaches to write
program. By using standard Java naming conventions they make their code
easier to read for themselves and for other programmers. Readability of Java
code is important because it means less time is spent trying to figure
out what the code does, and leaving more time to fix or modify it.
1. Every package name should exist a lower case latter.
Example
package student; // creating package
125
import java.lang; // import package

NAMING CONVERSION
2.First letter of every word of class name or interface name should
exists in upper case.
Example
class StudentDetails {
..... }
interface FacultyDetail {
..... }
3.Every constant value should exists in upper case latter. It is containing
more than one word than it should be separated with underscore (-).
Example
class Student {
final String COLLEGE_NAME="abcd";
126
.... }

NAMING CONVERSION
Note: if any variable is preceded by final keyword is known as
constant value.
Example
class Student {
Final String Student_name="abcd";
}
While declaring variable name, method, object reference the first letter
of first word should be exits in lower case but from the second words
onward the first letter should exists in upper case.
class Student {
String StudentName="xyz";
void instantStudentDetails();
{ .... .... }
127
Student final

According to CamelCase if name is combined with two words, second word will
start with uppercase letter always. General Example studentName,
customerAccount. In term of java programming e.g. actionPerformed(),
NAMING CONVERSION
CamelCase in java naming conventions
Java follows camelcase syntax for naming the class, interface, method and
variable.
128
firstName, ActionEvent, ActionListener etc.

Syntax
import package1.package2.......*;
IMPORT STATEMENT
Import statements in Java
Import is a keyword in java language used to import the predefined properties
of java API into current working java program.
129
Used to import all the predefined properties of given package.

Syntax
import pack1.package2.............Class_Name/Interface_Name;
Used to import specific class or interface in a java program.
Java API is a collection of package, package is a container which is collection of
predefined classes and interfaces.
Note: Import statement should be the first statement of the java programs.
130
IMPORT STATEMENT

Access Modifiers in Java
Access modifiers are those which are applied before data members or
methods of a class. These are used to where to access and where not to access
the data members or methods. In Java programming these are classified into
four types:
• Private
• Default (not a keyword)
• Protected
• Public
Note: Default is not a keyword (like public, private, protected are keyword) If
we are not using private, protected and public keywords, then JVM is by
default taking as default access modifiers.
131
ACCESS MODIFIERS

Note: Protected members of the class are accessible within the same class
and another class of same package and also accessible in inherited class of
132
another package.
ACCESS MODIFIERS
Access modifiers are always used for, how to reuse the features within the
package and access the package between class to class, interface to interface
and interface to a class. Access modifiers provide features accessing and
controlling mechanism among the classes and interfaces.

ACCESS MODIFIERS
Rules for access modifiers:
The following diagram gives rules for Access modifiers.
133

ACCESS MODIFIERS
private: Private members of class in not accessible anywhere in program these
are only accessible within the class. Private are also called class level access
modifiers.
Example
class Hello {
private int a=20;
private void show() {
System.out.println("Hello java"); } }
public class Demo {
{ Hello obj=new Hello();
System.out.println(obj.a); //Compile
Time Error, you can't access private
obj.show(); //Compile Time Error, you
can't access private methods
134
} }

{ Hello obj=new Hello();
System.out.println(obj.a);
Output
20
ACCESS MODIFIERS
public: Public members of any class are accessible anywhere in the program
in the same class and outside of class, within the same package and outside of
the package. Public are also called universal access modifiers.
Example
class Hello
{ public int
a=20;
public void show()
java"); } } public class Demo {
135
Hello Java
obj.show(); } }

ACCESS MODIFIERS
protected: Protected members of the class are accessible within the same class
and another class of the same package and also accessible in inherited class of
another package. Protected are also called derived level access modifiers.
In below the example we have created two packages pack1 and pack2. In pack1,
class A is public so we can access this class outside of pack1 but method show
is declared as a protected so it is only accessible outside of package pack1 only
through inheritance.
Example : // save A.java
package demo;
public class DEMO {
protected void
show() {
System.out.println("
Hello Java");
136
} }

//save B.java
package PACKAGE2;
import demo.*;
public class CLASS_2
extends DEMO {
{ CLASS_2 obj = new CLASS_2();
obj.show();
}
}
Output
Hello Java
ACCESS MODIFIERS
137

ACCESS MODIFIERS
default: Default members of the class are accessible only within the same class
and another class of the same package. The default are also called package level
access modifiers.
Example
//save by A.java
package demo;
public class DEMO
{ void show()
{
Hello Java");
}
}
138

//save by B.java
package PACKAGE2;
//import demo.*;
public class CLASS_2 {
public static void
main(String args[])
{
DEMO obj = new DEMO(); //Compile Time Error, can't access outside the
package
obj.show(); //Compile Time Error, can't access outside the package
}
}
Output
ACCESS MODIFIERS
Hello Java
139

ARRAY IN JAVA
Array is a collection of similar type of data. It is fixed in size means that you
can't increase the size of array at run time. It is a collection of homogeneous
data elements. It stores the value on the basis of the index value.
Advantage of Array
• One variable can store multiple value:
The main advantage of the array is we can represent multiple value
under the same name.
• Code Optimization:
No, need to declare a lot of variable of same type data, We can retrieve and
sort data easily.
• Random access:
We can retrieve any data from array with the help of the index value.
140

Disadvantage of Array
• The main limitation of the array is Size Limit when once we declare array
there is no chance to increase and decrease the size of an array according to
our requirement,
• Hence memory point of view array concept is not recommended to use. To
overcome this limitation in Java introduce the collection concept.
Types of Array
There are two types of array in Java.
• Single Dimensional Array
• Multidimensional Array
141
ARRAY IN JAVA

Array Declaration
Single dimension array declaration.
Syntax
1. int[] a;
2. int a[];
3. int []a;
Note: At the time of array declaration we cannot specify the size of the array.
For Example int[5] a; this is wrong.
2D Array declaration.
Syntax
1. int[][] a;
2. int a[][];
142
6. int []a[];
4. int[] a[];
3. int [][]a;
ARRAY IN JAVA
5. int[] []a;

int[] arr = new int[10];
(or)
int[] arr =
{10,20,30,40,50};
Accessing array
elements
143
Access the elements of array by using
index value of an elements.
Syntax - arrayname[n-1];
Access Array Elements
int[] arr={10,20,30,40};
System.out.println("Elemen
t at 4th place"+arr[2]);
// The size of array is 10.
ARRAY IN JAVA
Every array in a Java is an object, Hence we can create array by using new
keyword.
Syntax

Example of Array
public class ArrayEx {
public static void main(String []args)
{ int arr[] = {10,20,30};
for (int i=0; i < arr.length; i++)
{ System.out.println(arr[i]);
}
}
}
Output
10
20
30
ARRAY IN JAVA
144

Note:
1) At the time of array creation we must be specify the size of array otherwise
get an compile time error.
For Example
• int[] a=new int[]; Invalid.
• int[] a=new int[5]; Valid
2) If we specify the array size as negative int value, then we will get run-
time error, NegativeArraySizeException.
3) To specify the array size the allowed data types are byte, short, int, char If
we use other data type then we will get an Compile time error.
4) The maximum allowed size of array in Java is 2147483647 (It is the
maximum value of int data type)
145
ARRAY IN JAVA

ARRAY IN JAVA
Difference Between Length and Length() in Java
length: It is a final variable and only applicable for array. It represent size of
array.
Example
int[] a=new int[10];
System.out.println(a.length); // 10
System.out.println(a.length()); // Compile time error
length(): It is the final method applicable only for String objects.
It represents the number of characters present in the String.
Example
String s="Java";
System.out.println(s.length()); // 4
146
System.out.println(s.length); // Compile time error

Final keyword in java
It is used to make a variable as a constant, Restrict method overriding, Restrict
inheritance. It is used at variable level, method level and class level. In java
language final keyword can be used in following way.
• Final at variable level
• Final at method level
• Final at class level
FINAL KEYWORD
147

Final at variable level
Final keyword is used to make a variable as a constant. This is similar to const
in other language. A variable declared with the final keyword cannot be
modified by the program after initialization. This is useful to universal
constants, such as "PI".
Final Keyword in java Example
public class Circle {
public static final double PI=3.14159;
{
System.out.println(PI);
}
}
148
FINAL KEYWORD

Final at method level
• It makes a method final, meaning that sub classes can not override this
method. The compiler checks and gives an error if you try to override the
method.
• When we want to restrict overriding, then make a method as a final.
Example
public class A
{ public void fun1()
{
.......
}
public final void
fun2() {
.......
}
149
}
FINAL KEYWORD

class B extends A
{
public void fun1()
{
.......
}
public void fun2()
{
// it gives an error because we can not override final method
}
}
150
FINAL KEYWORD

FINAL KEYWORD
Example of final keyword at method level
class Employee
{
final void disp()
{
System.out.println("Hello Good Morning");
}
}
class Developer extends Employee
{ void disp()
{
System.out.println("How are you ?");
}
151
}

class FinalDemo
{
{
Developer obj=new Developer();
obj.disp();
}
}
Output
It gives an error
152
FINAL KEYWORD

Final at class level
It makes a class final, meaning that the class can not be inheriting by other
classes. When we want to restrict inheritance then make class as a final.
Example
public final class A
{
......
}
public class B extends A
{
// it gives an error, because
we can not inherit final class
}
153
FINAL KEYWORD

obj.show();
154
} }
Output:
It gives an error
FINAL KEYWORD
Example of final keyword at class level
final class Employee
{ int salary=10000;
}
class Developer
extends Employee {
void show() {
System.out.println("H
ello Good Morning");
} }
class FinalDemo {
public static void
main(String args[]) {

THIS KEYWORD
this is a reference variable that refers to the current object. It is a keyword in
java language represents current class object
Usage of this keyword
• It can be used to refer current class instance variable.
• this() can be used to invoke current class constructor.
• It can be used to invoke current class method (implicitly)
• It can be passed as an argument in the method call.
• It can be passed as argument in the constructor call.
• It can also be used to return the current class instance.
Why use this keyword in java?
The main purpose of using this keyword is to differentiate the formal
parameter and data members of class, whenever the formal parameter and
data members of the class are similar then JVM get ambiguity (no clarity
155
between formal parameter and member of the class)

To differentiate between formal parameter and data member of the class, the
data member of the class must be preceded by "this".
"this" keyword can be use in two ways. 1-
this . (this dot) 2 - this() (this off)
this . (this dot)
which can be used to differentiate
variable of class and formal parameters
of method or constructor.
"this" keyword are used for two purpose,
they are
It always points to current class
object.
• Whenever the formal parameter and data member of the class are similar and
JVM gets an ambiguity (no clarity between formal parameter and data
members of the class).
• To differentiate between formal parameter and data member of the class, the
156
THIS KEYWORD

THIS KEYWORD
Syntax - this.data member of current class.
Note: If any variable is preceded by "this" JVM treated that variable as class
variable.
Example without using this keyword
class Employee {
int id;
String name;
Employee(int id, String name)
{ id = id;
name = name;
}
void show()
{ System.out.println(id+"
"+name);
157
}

THIS KEYWORD
{
Employee e1 = new Employee(111,"Harry");
Employee e2 = new Employee(112,"Jacy");
e1.show();
e2.show();
}
}
Output:
0 null
0 null
158

THIS KEYWORD
In the above example, parameter (formal arguments) and instance variables
are same that is why we are using "this" keyword to distinguish between local
variable and instance variable.
Example of this keyword in java
class Employee {
int id;
String name;
Employee(int id,String name)
{ this.id = id;
this.name = name;
}
void show() {
System.out.println(id+"
"+name); 159
}

THIS KEYWORD
{ Employee e1 = new Employee(111,"Harry");
e1.show();
e2.show(); } }
Output
111 Harry
112 Jacy
Note 1: The scope of "this" keyword is
within the class.
Note 2: The main purpose of using "this" keyword in real life application is to
differentiate variable of class or formal parameters of methods or
constructor (it is highly recommended to use the same variable name
either in a class or method and constructor while working with similar
160
objects).

THIS KEYWORD
Difference between this and super keyword
Super keyword is always pointing to base class (scope outside the class)
features and "this" keyword is always pointing to current class (scope is within
the class) features.
Example when no need of this keyword
class Employee {
int id;
String name;
Employee(int i,String n)
{ id = i;
name = n;
}
void show() {
161
System.out.println(id+" "+name);

}
{ Employee e1 = new Employee(111,"Harry");
e1.show();
e2.show();
}
}
Output
111 Harry
112 Jacy
162
THIS KEYWORD

THIS KEYWORD
In the above example, no need of use this keyword because parameter (formal
arguments) and instance variables are different. This keyword is only use
when parameter (formal arguments) and instance variables are same.
this ()
which can be used to call one constructor within the another constructor
without creation of objects multiple time for the same class.
Syntax
this(); // call no parameterized or default constructor
this(value1,value2,.....) //call parameterize constructor
this keyword used to invoke current class method
(implicitly)
By using this keyword you can invoke the method of
the current class. If
you do not use the this keyword, compiler
automatically adds this keyword 163
at time of invoking of the method.

THIS KEYWORD
164

Example of this keyword
class Student {
void show()
{
System.out.prin
tln("You got
A+");
}
void marks()
{
165
}
//no need to use this here because compiler does it.
this.show();
}
void display()
{
show(); //compiler act marks() as this.marks()
THIS KEYWORD

Syntax
You got A+
166
THIS KEYWORD
{
Student s = new Student();
s.display();
}
}

Rules to use this()
this() always should be the first statement of the constructor. One
constructor can call only other single constructor at a time by using this().
THIS KEYWORD
167

Super keyword in java
Super keyword in java is a reference variable that is used to refer parent class
object. Super is an implicit keyword create by JVM and supply each and every
java program for performing important role in three places.
• At variable level
• At method level
• At constructor level
Need of super keyword:
Whenever the derived class is inherits the base class features, there is a
possibility that base class features are similar to derived class features and JVM
gets an ambiguity. In order to differentiate between base class features and
derived class features must be preceded by super keyword.
Syntax
168
super.baseclass features.
SUPER KEYWORD

Super at variable level:
Whenever the derived class inherit base class data members there is a
possibility that base class data member are similar to derived class data
member and JVM gets an ambiguity.
In order to differentiate between the data member of base class and derived
class, in the context of derived class the base class data members must be
preceded by super keyword.
Syntax
super.baseclass datamember name
if we are not writing super keyword before the base class data member name
than it will be referred as current class data member name and base
class data member are hidden in the context of derived class.
169
SUPER KEYWORD

HR obj=new HR();
obj.display();
170
Salary: 20000.0
} }
Output
SUPER KEYWORD
Program without using super keyword
class Employee
{ float
salary=10000;
}
class HR extends
Employee {
float salary=20000;
void display() {
Salary:
"+salary);//print
current class salary
} }
class Supervarible {
public static void
main(String[] args)

HR obj=new HR();
obj.display();
171
Salary: 10000.0
} }
Output
SUPER KEYWORD
Program using super keyword al variable level
class
Employee{ float
salary=10000;
}
class HR extends
Employee {
float salary=20000;
void display() {
Salary:
"+super.salary);//pr
int base class salary
} }
class Supervarible {
public static void
main(String[] args)

Super at method level
• The super keyword can also be used to invoke or call parent class method.
It should be use in case of method overriding. In other word super keyword
use when base class method name and derived class method name have
same name.
• In the below example Student and Faculty both classes have message()
method if we call message() method from Student class, it will call the
message() method of Student class not of Person class because priority of
local is high.
• In case there is no method in subclass as parent, there is no need to use
super. In the example given below message() method is invoked from
Student class but Student class does not have message() method, so you
can directly call message() method.
172
SUPER KEYWORD

SUPER KEYWORD
Example of super keyword at method level
class Student
{ void message()
{
System.out.printl
n("Good
Morning Sir");
}
}
class Faculty extends Student
{ void message()
System.out.println("Good
Morning Students");
}
void display() {
message();//will invoke or call
current class message()
173
}

Output
Good Morning Students
Good Morning Sir
174
SUPER KEYWORD
{ Student s=new Student();
s.display();
}
}

s.display();
}
175
Good Morning Sir
}
Output
SUPER KEYWORD
Program where super is not required
class Student
{ void message()
{
System.out.printl
n("Good
Morning Sir");
} }
class Faculty extends Student
{ void display() {
message();//will invoke or call
parent class message() method
}
{ Student s=new Student();

SUPER KEYWORD
Super at constructor level
The super keyword can also be used to invoke or call the parent class
constructor. Constructor are calling from bottom to top and executing from top
to bottom.
To establish the connection between base class constructor and derived
class constructors JVM provides two implicit methods they are:
Super()
Super(...)
Super()
Super()
It is used
for
calling
super
class
176

SUPER KEYWORD
Super keyword used to call base class constructor
Syntax
class Employee {
Employee() {
System.out.println("Employee class Constructor");
}
}
class HR extends Employee
{ HR() {
super(); //will invoke or call
parent class constructor
System.out.println("HR class
Constructor");
}
}
177

class Supercons {
{ HR obj=new HR();
}
}
Output
Employee class Constructor
HR class Constructor
Note: super() is added in
each class constructor
automatically by compiler
178
SUPER KEYWORD

In constructor, default constructor is provided by compiler automatically but it
also adds super() before the first statement of constructor. If you are creating
your own constructor and you do not have either this() or super() as the first
statement, compiler will provide super() as the first statement
179
of the constructor.
SUPER KEYWORD

Super(...)
Super(...) It is used for calling super class parameterize constructor from the
context of derived class constructor.
Important rules
Whenever we are using either super() or super(...) in the derived class
constructors the super always must be as a first executable statement in the
body of derived class constructor otherwise we get a compile time error.
Rule 1 and Rule 3
Whenever the derived class constructor want to call default constructor of base
class, in the context of derived class constructors we write super().
Which is optional to write because every base class constructor contains
single form of default constructor?
180
SUPER KEYWORD

Rule 2 and Rule 4
Whenever the derived class constructor wants to call parameterized
constructor of base class in the context of derived class constructor we must
write super(...). which is mandatory to write because a base class may contain
multiple forms of parameterized constructors.
The following diagram use possibilities of using super() and
super(........)
181
SUPER KEYWORD

Synchronized is a Modifier which is applicable for the method or block, we
SYNCHRONIZED KEYWORD
Synchronized Keyword in Java
Synchronized Keyword is used for when we want to allowed only one thread
at a time then use Synchronized modifier. If a method or block declared as a
Synchronized then at a time only one thread is allowed to operate on the given
object.
182
can not declare class or variable with this modifier.

SYNCHRONIZED KEYWORD
Advantage of Synchronized
The main advantage of Synchronized keyword is we can resolve data
inconsistency problem.
Dis-Advantage of Synchronized
The main dis-advantage of Synchronized keyword is it increased the waiting
time of thread and effect performance of the system, Hence if there is no
specific requirement it is never recommended to use synchronized keyword.
183

VOLATILE KEYWORD
Volatile Keyword in Java
• If the variable keep on changing such type of variables we have to declare
with volatile modifier.
• Volatile is a modifier applicable only for variables but not for method and
class.
• If a variable declared as volatile then for every thread a separate local copy
will be created.
• Every intermediate modification performed by that thread will takes place in
local copy instead of master copy.
• Once the value got finalized just before terminating the thread the master
copy value will be updated with local stable value.
Advantage of Volatile
The main advantage of Volatile keyword is we can resolve data
184
inconsistency problems.

VOLATILE KEYWORD
Dis-Advantage of Volatile
The main dis-advantage of Volatile keyword is, crating and maintaining a
separate copy for every thread, increases complexity of the programming and
effects performance of the system. Hence if there is no specific requirement it
is never recommended to use volatile keyword, and it is
almost outdated keyword.
Note: Volatile variable means its value keep on changing where as final
variable means its value never changes. Hence final-Volatile combination is
illegal combination for variables.
185

Static Block in Java
• Static block is a set of statements, which will be executed by the JVM before
execution of main method.
• At the time of class loading if we want to perform any activity we have to
define that activity inside static block because this block execute at the
time of class loading.
• In a class we can take any number of static block but all these blocks will be
execute from top to bottom.
STATIC BLOCK
186

Syntax
Static { ........
//Set of Statements ........
}
Note: In real time application static block can be used whenever we want to
execute any instructions or statements before execution of main method.
Example of Static Block
class StaticDemo {
Static {
System.out.println(
"Hello how are
u ?");
187
This is main()
} }
}
System.out.println("This is main()");
Output
Hello how are u ?
STATIC BLOCK

STATIC BLOCK
Run java program without main method
class StaticDemo {
static {
System.out.println(
"Hello how are
u ?");
}
}
Output:
Hello how are u ?
Exception is thread
"main"
java.lang.no-
suchmethodError:
Main
188

STATIC BLOCK
More than one static block in a program
class StaticDemo {
static
{
System.out.println(
"First static
block");
}
static
{
System.out.println(
"Second Static
block");
}
public static void
main(String
args[]) {
189
}

Output:
First static block
Second static block
This is main()
Note: "Here static block run according to there order (sequence by) from top to
bottom
Why a static block executes before the main method ?
A class has to be loaded in main memory before we start using it. Static block is
executed during class loading. This is the reason why a static block
executes before the main method.
190
STATIC BLOCK

INNER CLASSES
Inner Classes in Java Programming
If one class is existing within another class is known as inner class or nested
class
Syntax
class Outerclass_name {
.....
class Innerclass_name1{
.....
}
class Innerclass_name1{
.....
}
}
191

INNER CLASSES
The main purpose of using inner class
• To provide more security by making those inner class properties specific to
only outer class but not for external classes.
• To make more than one property of classes private properties.
• Private is a keyword in java language, it is preceded by any variable that
property can be access only within the class but not outside of it (provides
more security).
• If more than one property of class wants to make as private properties than
all can capped under private inner class.
Syntax
class Outerclass_name {
private class Innerclass_name {
..... //private properties
192
} }

Note: No outer class made as private class otherwise this is not available
for JVM at the time of execution.
Rules to access properties of inner classes
• Inner class properties can be accessed in the outer class with the object
reference but not directly.
• Outer class properties can be access directly within the inner class.
• Inner class properties can't be accessed directly or by creating directly
object.
Note: In special situation inner class property can be accessed in the external
class by creating special objects with the reference of its outer class.
193
INNER CLASSES

//outer class
194
Example
class A
{
void fun1() {
System.out.println("Hello fun1()");
// inner class properties should be access using
//object reference in outer class.
B ob=new B();
ob.x=10
System.out.println("x= "+ob.x);
ob.fun2();
}
INNER CLASSES

// inner class
195
}
// inner class variable
//inner class fun2()
class B
{
int x;
void fun2()
{
//outer class properties can be access directly
fun3();
}
}
INNER CLASSES
void fun3() // outer class fun3()
{
}

// external class
196
} }
class C
{
void fun3()
{
}
}
class IncDemo {
{ A oa=new A();
oa.fun1();
C oc=new C();
oc.fun3();
Output
Hello fun1()
X=10
Hello fun2()
Hello fun3()
INNER CLASSES

Accessing inner class properties in the external class
1. If inner class in non static the object can be created with the following syntax
Syntax
class Outer_class
{ class Inner_class
{
.....
}
.....
}
class
External_class {
Outer_class.Inner_Class objectrefernce=new Outer_Class.External_Class();
}
197
INNER CLASSES

2. If inner class is static the object reference can be created with the
following syntax
Syntax
class Outer_class { static
class Inner_Class {
.....
.....
}
}
class External_Class {
Outer_class.Inner_Class
objectrefernce=new
Outer_Class.External_Cla
ss();
}
}
198
INNER CLASSES

//Outer class
199
void fun2()
// non-static inner class
//inner class variable
//inner class fun1()
Example
class A
{
class B
{
int x;
void fun1()
fun1()");
}
}
static class C
{
int y=20;
//static inner class
// inner class variable
INNER CLASSES

{
}
}
}
class IncDemo {
B.ob=new A().new.B();
System.out.println(ob.x);
ob.fun1();
C. oc=new A.C();
System.out.println(oc.y);
oc.fun2();
} }
200
INNER CLASSES

Abstract class in Java
We know that every Java program must start with a concept of class that is
without the class concept there is no Java program perfect.
In Java programming we have two types of classes they are
• Concrete class
• Abstract class
Concrete class in Java
A concrete class is one which is containing fully defined methods or
implemented method.
Example
class Helloworld {
void display() {
System.out.println("Good Morning........");
201
} }
ABSTRACT CLASS

ABSTRACT CLASS
Here Helloworld class is containing a defined method and object can be created
directly.
Create an object
Helloworld obj=new Helloworld();
obj.display();
Every concrete class has specific
features and these classes are
used for
specific requirement, but not for
common requirement.
If we use concrete classes for fulfill common requirements than such
application will get the following limitations.
• Application will take more amount of memory space (main memory).
• Application execution time is more.
• Application performance is decreased.
To overcome above limitation you can use abstract class.
202

Abstract class in Java
A class that is declared with abstract keyword, is known as abstract class. An
abstract class is one which is containing some defined method and some
undefined method. In java programming undefined methods are known as un-
Implemented, or abstract method.
ABSTRACT CLASS
203

Syntax
abstract class className {
}
Example
abstract class A {
}
If any class have any abstract method then that class become an abstract class.
Example
class Vechile
{ abstract void
Bike();
}
Class Vechile is
become an abstract
class because it have
abstract Bike()
204
method.
ABSTRACT CLASS

…….
}
Abstract method
An abstract method is one which contains only declaration or prototype but it
never contains body or definition. In order to make any undefined method as
abstract whose declaration is must be predefined by abstract keyword.
Syntax
Example
abstract void sum();
abstract void diff(int, int);
ABSTRACT CLASS
Make class as abstract class
To make the class as abstract class, whose definition must be preceded by a
abstract keyword.
Example
abstract class Vechile {
205
abstract ReturnType methodName(List of formal parameter)

// abstract method
206
Speed limit is 40 km/hr..
//indirect object creation
Example of abstract class
abstract class Vechile
{ abstract void speed();
}
class Bike extends Vechile {
void speed() {
System.out.println("Speed
limit is 40 km/hr..");
}
{ Vachile obj = new Bike();
obj.speed();
} }
Output
ABSTRACT CLASS

ABSTRACT CLASS
Create an Object of abstract class
An object of abstract class cannot be created directly, but it can be created
indirectly. It means you can create an object of abstract derived class. You can see
in above example
Example - Vehicle obj = new Bike(); //indirect object creation
Abstract class of Java always contains common features.
• Every abstract class participates in inheritance.
• Abstract class definitions should not be made as final because abstract classes
always participate in inheritance classes.
• An object of abstract class cannot be created directly, but it can be created
indirectly.
• All the abstract classes of Java makes use of polymorphism along with method
overriding for business logic development and makes use of dynamic binding
207
for execution logic.

ABSTRACT CLASS
Advantage of abstract class
• Less memory space for the application
• Less execution time
• More performance
Why abstract class have no abstract static method ?
In abstract classes we have the only abstract instance method, but not
containing abstract static methods because every instance method is created
for performing repeated operation where as static method is created for
performing a one time operations in other word every abstract method is
instance but not static.
Abstract base class
An abstract base class is one which is containing physical representation of
abstract methods which are inherited by various sub classes.
208

Abstract derived class
• An abstract derived class is one which is containing logic representation of
abstract methods which are inherited from abstract base class with respect to
both abstract base class and abstract derived class one can not create objects
directly, but we can create their objects indirectly both abstract base class and
abstract derived class are always reusable by various sub classes. When the
derived class inherits multiple abstract method from abstract base class and if
the derived class is not defined at least one abstract method then the derived
class is known as abstract derived class and whose definition must be made as
abstract by using abstract keyword. (When the derived class becomes an
abstract derived class).
• If the derived class defined all the abstract methods which are inherited
from abstract Base class, then the derived class is known as concrete
209
derived class.
ABSTRACT CLASS

ABSTRACT CLASS
210

Vachile obj = new Bike();
obj.speed();
211
Speed limit is 40 km/hr..
obj.mileage(); } }
Output
Mileage is 60 km/ltr..
ABSTRACT CLASS
Example of abstract class having method body
abstract class Vehicle
{ abstract void speed();
void mileage() {
System.out.println("Mil
eage is 60 km/ltr..");
} }
class Bike extends Vehicle
{ void speed() {
System.out.println("Speed
limit is 40 km/hr..");
}

ABSTRACT CLASS
Example of abstract class having constructor, data member, methods
abstract class Vehicle
{ int limit=40;
Vechile() {
System.out.println("co
nstructor is invoked");
}
void getDetails() { System.out.println("it
has two wheels");
}
abstract void run();
}
class Bike extends Vehicle {
void run() { 212
System.out.println("running safely..");

}
{ Vachile obj = new Bike();
obj.run();
obj.getDetails();
System.out.println(obj.limit);
}
}
Output
constructor is invoked
running safely..
it has two wheels
213
40
ABSTRACT CLASS

214
DIFFERENCE BETWEEN ABSTRACT CLASS AND CONCRETE CLASS
Concrete class Abstract class
A Concrete class is used for specific
requirement
Abstract class is used to fulfill a common
requirement.
Object of concrete class can create directly.
Object of an abstract class can not create directly
(can create indirectly).
Concrete class containing fully defined
methods or implemented method.
Abstract class has both undefined method and
defined method.

215
some time it can be accessed with object reference.
DIFFERENCE BETWEEN STATIC AND NON-STATIC VARIABLE IN JAVA
The variable of any class are classified into two types;
• Static or class variable
• Non-static or instance variable
Static variable in Java
Memory for static variable is created only one in the program at the time of
loading of class. These variables are preceded by static keyword. static variable
can access with class reference.
Non-static variable in Java
Memory for non-static variable is created at the time of create an object of
class. These variable should not be preceded by any static keyword Example:
These variables can access with object reference.
Difference between non-static and static variable
Note: static variable not only can be access with class reference but also

216
Non-static variable Static variable
1
These variable should not be
preceded by any static keyword
Example:
class A{int a;}
These variables are preceded by static
keyword.
Example
class A{static int b;}
2
Memory is allocated for these
variable whenever an object is
created
Memory is allocated for these variable at
the time of loading of the class.
3 Memory is allocated multiple time
whenever a new object is created.
Memory is allocated for these variable
only once in the program.
4
Non-static variable also known as
instance variable while because
memory is allocated whenever
instance is created.
Memory is allocated at the time of
loading of class so that these are also
known as class variable.
5
Non-static variable are specific to an
object
Static variable are common for every object
that means there memory location can be
sharable by every object reference or same
class.
6
Non-static variable can access with
object reference.
Syntax
obj_ref.variable_name
Static variable can access with class
reference.
Syntax
class_name.variable_name

217
Example of static and non-static variable.
class Student {
int roll_no;
float marks;
String name;
static String
College_Name
="ITM";
}
class
StaticDemo {
public static
void
main(String
args[])
{
Student s1=new Student();
s1.roll_no=100;

218
s2.roll_no=200; s2.marks=75.8f;
s2.name="zyx";
System.out.println(s2.roll_no);
System.out.println(s2.marks);
System.out.println(s2.name);
System.out.println(Student.Coll
ege_Name);
} }
Output
100
65.8
abcd
ITM
200
75.8
zyx
ITM
System.out.println(s1.roll_no);
System.out.println(s1.marks);
System.out.println(s1.name);
System.out.println(Student.College_Name);
//or System.out.println(s1. College_Name);
but first is use in real time.

219
Note: In the above example College_Name variable is commonly sharable
by both S1 and S2 objects.

220
//will get memory when instance is created
int count=0;
Counter()
{ count++;
System.out.p
rintln(count
);
}
Understand static and non-static variable using counter
Program of counter without static variable
In this example, we have created an instance variable named count which is
incremented in the constructor. Since instance variable gets the memory at
the time of object creation, each object will have the copy of the instance
variable, if it is incremented, it won't reflect to other objects. So each objects
will have the value 1 in the count variable.
Example
class Counter {

Output
1
1
1
221
{
Counter c1=new Counter();
}
}

//will get memory only once
3
222
} }
static int count=0;
Counter()
{ count++;
System.out.println
(count); }
{ Counter c1=new Counter();
Output
1
2
Program of counter by static variable
As we have mentioned above, static variable will get the memory only once, if
any object changes the value of the static variable, it will retain its value.
Example
class Counter {

Non-Static method Static method
These method never be preceded by
static keyword
Example:
void fun1()
{
......
......
}
These method always preceded by static
keyword
Example:
static
void
fun2()
{
......
......
}
223
DIFFERENCE BETWEEN STATIC AND NON-STATIC METHOD IN JAVA
Difference between Static and non-static method in Java
In case of non-static method memory is allocated multiple time whenever
method is calling. But memory for static method is allocated only once at the
time of class loading. Method of a class can be declared in two different ways
• Non-static methods
• Static methods
Difference between non-static and static Method

224
Non-Static method Static method
Memory is allocated multiple time whenever
method is calling.
Memory is allocated only once at the time of class
loading.
It is specific to an object so that these are also
known as instance method.
These are common to every object so that it is also
known as member method or class method.
These methods always access with object
reference
Syntax:
Objref.methodname();
These property always access with class
reference
Syntax:
className.methodname();
If any method wants to be execute multiple
time that can be declare as non static.
If any method wants to be execute only once in
the program that can be declare as static .
Note: In some cases static methods not only can access with class reference
but also can access with object reference.

225
Example of Static and non-Static Method
class A
{ void fun1()
{
System.out.p
rintln("Hello
I am Non-
Static");
}
static void fun2()
{ System.out.println("Hello I am
Static");
} }
class Person {
{ A oa=new A();
// non static method
// static method
oa.fun1();
A.fun2();
} }
Output
Hello I am Non-Static
Hello I am Static

226
Following table represent how the static and non-static properties are
accessed in the different static or non-static method of same class or other
class.

227
Program to accessing static and non-static properties.
Example
class A {
int y;
void f2()
{
System.o
ut.println
("Hello
f2()");
}
}
class B
{ int z;
void f3(){
System.ou
t.println(

} }
class Sdemo
{ static int x;
static void f1(){
System.out.prin
tln("Hello
f1()");
}
{ x=10;
System.out.println("x="+x);
f1();
System.out.println("Hello
main");
B b1=new B();
b1.f3();
228
} }

CONSTRUCTOR IN JAVA
• constructor in Java is a special member method which will be called
implicitly (automatically) by the JVM whenever an object is created for
placing user or programmer defined values in place of default values. In a
single word constructor is a special member method which will be called
automatically whenever object is created.
• The purpose of constructor is to initialize an object called object
initialization. Constructors are mainly create for initializing the object.
Initialization is a process of assigning user defined values at the time of
allocation of memory space.
Syntax
className() {
.......
.......
229
}

CONSTRUCTOR IN JAVA
Advantages of constructors in Java
• A constructor eliminates placing the default values.
• A constructor eliminates calling the normal or ordinary method implicitly.
How Constructor eliminate default values ?
Constructor are mainly used for eliminate default values by user defined
values, whenever we create an object of any class then its allocate memory for
all the data members and initialize there default values. To eliminate these
default values by user defined values we use constructor.
230

231
Constructor Example in Java
class Sum {
int a,b;
Sum()
{ a=10;
b=20;
}
public static void main(String s[])
{ Sum s=new Sum();
c=a+b;
System.out.println("Sum: "+c);
} }
Output
Sum: 30
In above example when we create an
object of "Sum" class then constructor
of this class call and initialize user
defined value in a=10 and b=20. if we
can not create constructor of Sum
class then it print " Sum: 0 " because
default values of integer is zero.
CONSTRUCTOR IN JAVA

• Constructor will be called automatically when the object is created.
• Constructor name must be similar to name of the class.
• Constructor should not return any value even void also. Because basic aim is
to place the value in the object. (if we write the return type for the
constructor then that constructor will be treated as ordinary method).
• Constructor definitions should not be static. Because constructors will be
called each and every time, whenever an object is creating.
• Constructor should not be private provided an object of one class is created in
another class (Constructor can be private provided an object of one class
created in the same class).
• Constructors will not be inherited from one class to another class (Because
every class constructor is create for initializing its own data members).
• The access specifies of the constructor may or may not be private.
232
Rules or properties of a constructor

233
Method Constructor
1 Method can be any user defined name Constructor must be class name
2 Method should have return type It should not have any return type (even void)
3
Method should be called explicitly either
with object reference or class reference
It will be called automatically whenever object
is created
4
Method is not provided by compiler in any
case.
The java compiler provides a default
constructor if we do not have any constructor.
CONSTRUCTOR IN JAVA
• If the access specifier of the constructor is private then an object of
corresponding class can be created in the context of the same class but not
in the context of some other classes.
• If the access specifier of the constructor is not private then an object of
corresponding class can be created both in the same class context and in
other class context.
Difference between Method and Constructor

234
CONSTRUCTOR IN JAVA
Types of constructors
Based on creating objects in Java constructor are classified in two types. They
are
• Default or no argument Constructor
• Parameterized constructor.
Default Constructor
A constructor is said to be default constructor if and only if it never take any
parameters.
If any class does not contain at least one user defined constructor than the
system will create a default constructor at the time of compilation it is known
as system defined default constructor.

// Call default constructor
235
contain any user defined constructor.
// Initialization
.....
clsname ()
{
Block of statements;
}
.....
}
Note: System defined default constructor is created by java compiler and does
not have any statement in the body part. This constructor will be executed
every time whenever an object is created if that class does not
CONSTRUCTOR IN JAVA
Syntax of Default Constructor
class className
{

//TestDemo.java
236
};
Example:
class Test {
int a, b;
Test () {
System.out.println("I am from default Constructor...");
a=10;
b=20;
System.out.println("Value of a: "+a);
System.out.println("Value of b: "+b);
}
CONSTRUCTOR IN JAVA
Example of default constructor.
In below example, we are creating the no argument constructor in the Test
class. It will be invoked at the time of object creation.

class TestDemo {
public static void main(String [] args)
{ Test t1=new Test ();
}
};
237
Output:
I am from default Constructor...
Value of a: 10
Value of b: 20
CONSTRUCTOR IN JAVA

Rule-1:
Whenever we create an object only with default constructor, defining the
default constructor is optional. If we are not defining default constructor of a
class, then JVM will call automatically system defined default constructor. If
we define, JVM will call user defined default constructor.
Purpose of default constructor?
Default constructor provides the default values to the object like 0, 0.0, null etc.
depending on their type (for integer 0, for string null).
Explanation: In the below class, we are not creating any constructor so
compiler provides a default constructor. Here 0, 0.0 and null values are
provided by default constructor.
238
CONSTRUCTOR IN JAVA

239
s1.show(); } }
} }
class TestDemo {
public static void main(String [] args) {
CONSTRUCTOR IN JAVA
Example of default constructor that displays the default values
class Student {
int roll;
float marks;
String name;
void show() { System.out.println("Roll:
"+roll); System.out.println("Marks:
"+marks); System.out.println("Name:
"+name);
Output
Roll: 0
Marks: 0.0
Name: null

//parameterized constructor
240
new ClassName(value1, value2,.....);
ClassName(list of parameters) {
}
}
Syntax to call parametrized constructor
ClassName objref=new ClassName(value1, value2,.....);
OR
CONSTRUCTOR IN JAVA
parameterized constructor
If any constructor contain list of variable in its signature is known as
parameterized constructor. A parameterized constructor is one which takes
some parameters.
Syntax
class ClassName
{

CONSTRUCTOR IN JAVA
Example of Parameterized Constructor
class Test {
int a, b;
Test(int n1,
int n2) {
System.out.
println("I
am from
Parameteri
zed
Constructo
r...");
a=n1;
b=n2;
System.out.println("Value of a = "+a);
System.out.println("Value of b = "+b);
} };
class TestDemo1 {
241
} };

CONSTRUCTOR IN JAVA
Important points Related to Parameterized Constructor
• Whenever we create an object using parameterized constructor, it must be
define parameterized constructor otherwise we will get compile time error.
Whenever we define the objects with respect to both parameterized
constructor and default constructor, It must be define both the constructors.
• In any class maximum one default constructor but 'n' number of
parameterized constructors.
242

CONSTRUCTOR IN JAVA
Example of default constructor, parameterized constructor and
overloaded constructor
class Test {
int a, b;
Test () {
Syso("I am from default Constructor...");
a=1;
b=2;
System.out.println("Value of a ="+a);
System.out.println("Value of b ="+b);
}
Test (int x, int y) {
System.out.println("I am from double
Paraceterized Constructor"); 243

a=x;
b=y;
}
Test (int x) {
System.out.println("I am from single Parameterized Constructor");
a=x;
b=x;
}
Test (Test T) { 244
System.out.println("I am from Object Parameterized Constructor...");
CONSTRUCTOR IN JAVA

a=T.a;
b=T.b;
} };
class TestDemo2
{
public static void main (String k [])
{
Test t1=new Test ();
245
} };
Test t2=new Test (10, 20);
Test t3=new Test (1000);
Test t4=new Test (t1);
Note : By default the parameter passing
mechanism is call by reference.
CONSTRUCTOR IN JAVA

CONSTRUCTOR IN JAVA
Constructor Overloading
• Constructor overloading is a technique in Java in which a class can have
any number of constructors that differ in parameter lists. The compiler
differentiates these constructors by taking the number of parameters, and
their type.
• In other words whenever same constructor is existing multiple times in the
same class with different number of parameters or order of parameters or
type of parameters is known as Constructor overloading.
• In general constructor overloading can be used to initialized same or
different objects with different values.
Why overriding is not possible at constructor level.
The scope of constructor is within the class so that it is not possible to
246
achieved overriding at constructor level.

Syntax
class ClassName
{ ClassName() {
..........
..........
}
ClassName(dataty
pe1 value1) {.......
}
ClassName(dataty
pe1 value1,
datatype2 value2)
{.......
}
ClassName(dataty
pe2 variable2) {.......
}
247
} }
CONSTRUCTOR IN JAVA

Relationship in Java
Type of relationship always makes to understand how to reuse the feature from
one class to another class. In java programming we have three types of
relationship they are.
• Is-A Relationship
• Has-A Relationship
• Uses-A Relationship
Is-A relationship
• In Is-A relationship one class is obtaining the features of another class by
using inheritance concept with extends keywords.
• In a IS-A relationship there exists logical memory space
248
RELATIONSHIP

Example of Is-A Relation
class Faculty {
float salary=30000;
}
class Science extends Faculty {
float bonous=2000;
{ Science obj=new Science();
System.out.println("Salary is:"+obj.salary);
System.out.println("Bonous is:"+obj.bonous);
} }
Output
Salary is: 30000.0
249
Bonous is: 2000.0
RELATIONSHIP

250
Output
Salary is:
30000.0
Has-A relationship
• In Has-A relationship an object of one class is created as data member in
another class the relationship between these two classes is Has-A.
• In Has-A relationship there existed physical memory space and it is also
known as part of or kind of relationship.
Example of Has-A Relation
class Employee {
float salary=30000; }
class Developer extends Employee
{ float bonus=2000;
public static void main(String
args[]) {
Employee obj=new Employee();
System.out.println("Salary
is:"+obj.salary);
} }
RELATIONSHIP

Uses-A relationship
• A method of one class is using an
object of
relationship
class
the these
two
classes is
another
between
known as Uses-A
relationship.
• As long as the method is execution
the object space (o1) exists and once
the method execution is completed
automatically object memory space
will be destroyed.
RELATIONSHIP
251

Example
class Employee {
class Salary extends Employee {
void disp() {
float bonous=1000;
float Total=obj.salary+bonous;
System.out.println("Total Salary
is:"+Total);
} }
class Developer {
args[]) {
Salary s=new Salary();
Total Salary is: 31000.0 252
s.disp(); } }
RELATIONSHIP
Output

Note 1: The default relationship in java is Is-A because for each and every class
in java there exist an implicit predefined super class is java.lang.Object.
Note 2: The universal example for Has-A relationship is System.out (in
System.out statement, out is an object of printStream class created as static
data member in another system class and printStream class is known as Has-A
relationship).
Note 3: Every execution logic method (main() ) of execution logic is making
use of an object of business logic class and business logic class is known as
Uses-A relationship.
253
RELATIONSHIP

OOP's Concept in Java
Object-Oriented Programming is a methodology or paradigm to design a
program using classes and objects.
• Object
• Class
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation
OOPS CONCEPT
254

Object
Object is the physical as well as logical entity where as class is the only logical
entity.
Class
Class is a blue print which is containing only list of variables and method and
no memory is allocated for them. A class is a group of objects that has common
properties.
Encapsulation
Encapsulation is a process of wrapping of data and methods in a single
unit is called encapsulation. Encapsulation is achieved in C++ language by
class concept. The main advantage of using of encapsulation is to secure the
data from other methods, when we make a data private then these data only
use within the class, but these data not accessible outside the class.
255
OOPS CONCEPT

required
256
essential
Abstraction
Abstraction is the concept of exposing only the
characteristics and behavior with respect to a context.
Hiding of data is known as data abstraction. In object oriented programming
language this is implemented automatically while writing the code in the form
of class and object.
Inheritance
The process of obtaining the data members and methods from one class to
another class is known as inheritance. It is one of the fundamental features of
object-oriented programming.
OOPS CONCEPT

Polymorphism
The process of representing one Form in multiple forms is known as
Polymorphism. Here one form represent original form or original method
always resides in base class and multiple forms represents overridden method
which resides in derived classes.
Note: All these concept I will discuss in detail later.
257
OOPS CONCEPT

Inheritance in Java
The process of obtaining the data members and methods from one class to
another class is known as inheritance. It is one of the fundamental features of
object-oriented programming
Important points
• In the inheritance the class which is give data members and methods is
known as base or super or parent class.
• The class which is taking the data members and methods is known as sub or
derived or child class.
• The data members and methods of a class are known as features.
• The concept of inheritance is also known as re-usability or extendable
classes or sub classing or derivation.
258
INHERITANCE

Why use Inheritance ?
• For Method Overriding (used for Runtime Polymorphism).
• It's main uses are to enable polymorphism and to be able to reuse code for
different classes by putting it in a common super class
• For code Re-usability
Syntax of Inheritance
class Subclass-Name extends Superclass-Name
{
//methods and fields
}
Real Life Example of Inheritance in Java
The real life example of inheritance is child and parents, all the properties
INHERITANCE
259
of father are inherited by his son.

In the above diagram data members and methods are represented in broken
line are inherited from faculty class and they are visible in student
260
class logically.
INHERITANCE
The following diagram use view about inheritance.

Advantage of inheritance
If we develop any application using concept of Inheritance than that
application have following advantages,
• Application development time is less.
• Application take less memory.
• Application execution time is less.
• Application performance is enhance (improved).
• Redundancy (repetition) of the code is reduced or minimized so that we get
consistence results and less storage cost.
Note: In Inheritance the scope of access modifier increasing is allow but
decreasing is not allow. Suppose in parent class method access modifier is
default then it's present in child class with default or public or protected
access modifier but not private(it decreased scope).
261
INHERITANCE

Types of Inheritance
Based on number of ways inheriting the feature of base class into derived
class we have five types of inheritance; they are:
• Single inheritance
• Multiple inheritance
• Hierarchical inheritance
• Multilevel inheritance
• Hybrid inheritance
262
INHERITANCE

Single inheritance
In single inheritance there exists single base class and single derived class.
Example of Single Inheritance
class Faculty {
class Science extends
Faculty{ float bonus=2000;
System.out.println("Bonus is:"+obj.bonus);
} }
Output
INHERITANCE
263
Salary is: 30000.0 Bonus is: 2000.0

INHERITANCE
Multilevel inheritances in Java
In Multilevel inheritances there exists
single base class, single derived class
and multiple intermediate base classes.
Single base class + single derived
class + multiple intermediate base
classes.
Intermediate base classes
An intermediate base class is one in one
context with access derived class
and in another context same class
access base class.
264

INHERITANCE
Example of Multilevel Inheritance
class Faculty
{
float total_sal=0, salary=30000;
}
class HRA extends Faculty
{
float hra=3000;
}
class DA extends HRA
{
float da=2000;
}
265

class Science extends DA
{
float bonous=2000;
{
Science obj=new Science();
obj.total_sal=obj.salary+obj.hra+obj.da+obj.bonous;
System.out.println("Total Salary is:"+obj.total_sal);
}
}
Output
Total Salary is: 37000.0
266

Multiple inheritance
In multiple inheritance there exist multiple classes and single derived class.
The concept of multiple inheritance is not supported in java through
concept of classes but it can be supported through the concept of interface.
267
INHERITANCE

Hybrid inheritance
• Combination of any inheritance type
• In the combination if one of the combination is multiple inheritance then
the inherited combination is not supported by java through the classes
concept but it can be supported through the concept of interface.
INHERITANCE
268

INHERITANCE
Inheriting the feature from base class to derived class
In order to inherit the feature of base class into derived class we use the
following syntax
Syntax
class ClassName-2 extends ClasssName-1
{
variable declaration;
Method declaration;
}
Explanation
• ClassName-1 and
ClassName-2
represents name
of the base and
derived
classes
respectively.
class into derived class it improves the functionality of derived class.269

INHERITANCE
Important Points for Inheritance:
In java programming one derived class can extends only one base class because
java programming does not support multiple inheritance through the concept
of classes, but it can be supported through the concept of Interface. Whenever
we develop any inheritance application first create an object of bottom most
derived class but not for top most base class.
When we create an object of bottom most derived class, first we get the
memory space for the data members of top most base class, and then we get the
memory space for data member of other bottom most derived class. Bottom
most derived class contains logical appearance for the data members of all top
most base classes.
If we do not want to give the features of base class to the derived class then the
definition of the base class must be preceded by final hence final base
270
classes are not reusable or not inheritable.

INHERITANCE
• If we are do not want to give some of the features of base class to derived class
than such features of base class must be as private hence private features of
base class are not inheritable or accessible in derived class.
• Data members and methods of a base class can be inherited into the
derived class but constructors of base class can not be inherited because
every constructor of a class is made for initializing its own data members but
not made for initializing the data members of other classes.
• An object of base class can contain details about features of same class but an
object of base class never contains the details about special features of its
derived class (this concept is known as scope of base class object).
• For each and every class in java there exists an implicit predefined super
class called java.lang.Object. because it providers garbage collection
facilities to its sub classes for collecting un-used memory space and
271
improved the performance of java application.

Example of Inheritance
class Faculty {
float salary=30000;
}
class Science extends Faculty {
float bonus=2000;
System.out.println("Bonus is:"+obj.bonus);
} }
Output
Salary is: 30000.0
272
Bonus is: 2000.0
INHERITANCE

INHERITANCE
Why multiple inheritance is not supported in java?
Due to ambiguity problem java does not support multiple inheritance at class
level.
Example
class A
{
void disp()
{
System.out.println("Hello");
}
}
class B
{
273
void disp()

//Now which disp() method would be invoked?
274
level.
obj.disp();
}
}
In above code we call both class A and class B disp() method then it confusion
which class method is call. So due to this ambiguity problem in java do not use
multiple inheritance at class level, but it support at interface
INHERITANCE
}
}
class C extends A,B { //suppose if it were
Public Static void main(String args[])
{
C obj=new C();

INHERITANCE
Difference between Java Inheritance and C++ Inheritance
The main difference between java Inheritance and C++ Inheritance is; Java
doesn’t support multiple inheritance but C++ support.
275

METHOD OVERLOADING
Method Overloading in Java
Whenever same method name is exiting multiple times in the same class with
different number of parameter or different order of parameters or different
types of parameters is known as method overloading.
276

METHOD OVERLOADING
Why use method Overloading in Java ?
• Suppose we have to perform addition of given number but there can be any
number of arguments, if we write method such as a(int, int)for two
arguments, b(int, int, int) for three arguments then it is very difficult for
you and other programmer to understand purpose or behaviors of method
they can not identify purpose of method.
• So we use method overloading to easily figure out the program. For example
above two methods we can write sum(int, int) and sum(int, int, int) using
method overloading concept.
Syntax
class class_Name
{
Returntype method() {
277
.........

}
Returntype method(datatype1 variable1) {
.........
}
Returntype method(datatype1 variable1, datatype2 variable2) {
.........
}
Returntype method(datatype2 variable2) {
.........
}
Returntype method(datatype2 variable2, datatype1 variable1) {
.........
}
278
}
METHOD OVERLOADING

By changing number of arguments
In this example, we have created two overloaded methods, first sum method
performs addition of two numbers and second sum method performs addition
of three numbers.
279
Different ways to overload the method
There are two ways to overload the method in java
• By changing number of arguments or parameters
• By changing the data type
METHOD OVERLOADING

obj.sum(10, 20);
obj.sum(10, 20, 30);
}
280
60
}
Output
30
METHOD OVERLOADING
Example Method Overloading in Java
class Addition {
void sum(int a, int b)
{ System.out.println(a+b
);
}
void sum(int a, int b, int c) {
System.out.println(a+b+c);
}
{ Addition obj=new Addition();

METHOD OVERLOADING
By changing the data type
In this example, we have created two overloaded methods that differs in data
type. The first sum method receives two integer arguments and second sum
method receives two float arguments.
Example Method Overloading in Java
class Addition {
void sum(int a, int b)
{
System.out.println(a+b);
}
void sum(float a, float b)
{
281
}

{
Addition obj=new Addition();
obj.sum(10, 20);
obj.sum(10.05, 15.20);
}
}
Output
30
25.25
282

METHOD OVERLOADING
Why Method Overloading is not possible by changing the return type of
method?
In java, method overloading is not possible by changing the return type of the
method because there may occur ambiguity. Let's see how ambiguity may
occur: because there was problem:
Example of Method Overloading
class Addition
{
int sum(int a, int b)
{
}
double sum(int a, int b)
283
{

//Compile Time Error
284
}
{
Addition obj=new Addition();
int result=obj.sum(20,20);
}
}

Explanation of Code
Example
int result=obj.sum(20,20);
Here how can java determine which sum() method should be called
Note: The scope of overloading is within the class.
Any object reference of class can call any of overloaded method.
Can we overload main() method ?
• Yes, We can overload main() method. A Java class can have any number of
main() methods.
• But run the java program, which class should have main() method with
signature as "public static void main(String[] args).
• If you do any modification to this signature, compilation will
be
successful. But, not run the java program. 285
• we will get the run time error as main method not found.
METHOD OVERLOADING

METHOD OVERLOADING
Example of overload main() method
public class mainclass {
{ System.out.println("Execution starts from Main()");
}
void main(int args)
{ System.out.println("Override
main()");
}
double main(int i, double d)
{ System.out.println("Override
main()"); return d;
} }
Output 286
Execution starts from Main()

METHOD OVERRIDING
Method Overriding in Java
Whenever same method name is existing in both base class and derived class
with same types of parameters or same order of parameters is known as
method Overriding. Here we will discuss about Overriding in Java.
Note: Without Inheritance method overriding is not possible.
Advantage of Java Method Overriding
• Method Overriding is used to provide specific implementation of a method
that is already provided by its super class.
• Method Overriding is used for Runtime Polymorphism
Rules for Method Overriding
• method must have same name as in the parent class.
• method must have same parameter as in the parent class.
• must be IS-A relationship (inheritance).
287

288
that is why we use method overriding.
Output : Man walking
Man obj = new Man();
obj.walk();
} }
Problem is that I have to providea specific
implementation of walk() method in
subclass
METHOD OVERRIDING
Understanding the problem without method overriding
Lets understand the problem that we may face in the program if we do not
use method overriding.
Example Method Overriding in Java
class Walking {
void walk(){
System.out.println("Man walking fastly");
} }
class OverridingDemo {

METHOD OVERRIDING
Example of method overriding in Java
In this example, we have defined the walk method in the subclass as defined in
the parent class but it has some specific implementation. The name and
parameter of the method is same and there is IS-A relationship between the
classes, so there is method overriding.
Example
class Walking
{
void walk()
{
System.out.println("Man walking fastly");
}
}
289

290
}
obj.walk();
}
METHOD OVERRIDING
class Man extends walking
{
void walk()
{
System.out.println("Man walking slowly");
}
}
class OverridingDemo
{
{ Man obj = new Man();
Output
Man walking slowly

METHOD OVERRIDING
Note: Whenever we are calling overridden method using derived class object
reference the highest priority is given to current class (derived class). We can
see in the above example high priority is derived class.
Note: super. (super dot) can be used to call base class overridden method
in the derived class.
291

METHOD OVERRIDING
Accessing properties of base class with respect to derived class object
class A {
int x;
void f1()
{
x=10;
System.o
ut.printl
n(x);
}
void f4()
{ System.out.println("this is
f4()");
System.out.println("-----------------
");
} };
class B extends A {
292
void f1() {

int y=20;
System.out.println(y);
System.out.println("this is f1()");
System.out.println("---------------");
}
};
class C extends A {
int z;
void f1() {
z=10;
System.ou
t.println(z
);
System.ou
t.println("
this is
f1()");
293
};
METHOD OVERRIDING

class Override
{
{
A a1=new B();
a1.f1();
a1.f4();
A c1=new C();
c1.f1();
c1.f4();
}
}
294
METHOD OVERRIDING

METHOD OVERRIDING
Example of Implement overriding concept
class Person {
String name;
void
sleep(String
name) {
this.name=na
me;
System.out.pri
ntln(this.nam
e +"is
sleeping+8hr/
day");
}
void walk()
{ System.out.println("this is
walk()");
System.out.println("-----------------");
295
System.out.println("only student write the exam");

296
}
void sleep(String name)
{ super.name=name;
System.out.println(super.n
ame +"is sleeping
6hr/day");
System.out.println("--------
----------");
} };
class Developer extends Person
{ public void designProj() {
System.out.println("Design the
project");
}
void sleep(String name) {
super.name=name;
System.out.println(super.name +"is sleeping 4hr/day");
METHOD OVERRIDING

297
METHOD OVERRIDING
}
};
class OverideDemo
{ Student s1=new Student();
s1.writExams();
s1.sleep("student");
s1.walk();
Developer d1=new Developer();
d1.designProj();
d1.sleep("developer");
}
}

298
Overloading Overriding
1
Whenever same method or Constructor
is existing multiple times within a class
either with different number of
parameter or with different type of
parameter or with different order of
parameter is known as Overloading.
Whenever same method name is existing
multiple time in both base and derived
class with same number of parameter or
same type of parameter or same order of
parameters is known as Overriding.
2
Arguments of method must be different
at least arguments.
Argument of method must be same
including order.
3 Method signature must be different. Method signature must be same.
4
Private, static and final methods can be
overloaded.
Private, static and final methods can not
be override.
5
Access modifiers point of view no
restriction.
Access modifiers point of view not
reduced scope of Access modifiers but
increased.
6
Also known as compile time
polymorphism or static polymorphism
or early binding.
Also known as run time polymorphism
or dynamic polymorphism or late
binding.
METHOD OVERLOADING vs. OVERRIDING

299
Overloading Overriding
7
Overloading can be exhibited both are
method and constructor level.
Overriding can be exhibited only at
method label.
8
The scope of overloading is within the
class.
The scope of Overriding is base class
and derived class.
9
Overloading can be done at both static
and non-static methods.
Overriding can be done only at non-
static method.
10
For overloading methods return type may
or may not be same.
For overriding method return type
should be same.
Note: In overloading we have to check only methods names (must be same)
and arguments types (must be different) except these the remaining like
return type access modifiers etc. are not required to check But in overriding
every things check like method names arguments types
return types access modifiers etc.
METHOD OVERLOADING vs. OVERRIDING

INTERFACE IN JAVA
Interface is similar to class which is collection of public static final variables
(constants) and abstract methods.
The interface is a mechanism to achieve fully abstraction in java. There can be
only abstract methods in the interface. It is used to achieve
fully
abstraction and multiple inheritance in Java.
Why we use Interface ?
• It is used to achieve fully abstraction.
• By using Interface, you can achieve multiple inheritance in java.
• It can be used to achieve loose coupling.
properties of Interface
• It is implicitly abstract. So we no need to use the abstract keyword when
declaring an interface.
• Each method in an interface is also implicitly abstract, so the abstract 300
keyword is not needed.

INTERFACE IN JAVA
• Methods in an interface are implicitly public.
• All the data members of interface are implicitly public static final.
How interface is similar to class ?
Whenever we compile any Interface program it generate .class file. That
means the bytecode of an interface appears in a .class file.
How interface is different from class ?
• You can not instantiate an interface.
• It does not contain any constructors.
• All methods in an interface are abstract.
• Interface can not contain instance fields. Interface only contains public static
final variables.
• Interface is can not extended by a class; it is implemented by a class.
• Interface can extend multiple interfaces. It means interface
support 301
multiple inheritance

In the above image when we compile any interface program, by default
compiler added public static final before any variable and public abstract
before any method. Because Interface is design for fulfill universal
302
requirements and to achieve fully abstraction.
INTERFACE IN JAVA
Behavior of compiler with Interface program

Declaring Interfaces:
The interface keyword is used to declare an interface.
Example
interface Person {
datatype variablename=value;
//Any number of final, static fields
returntype methodname(list of parameters or no parameters)
//Any number of abstract method declarations
}
Explanations
In the above syntax Interface is a keyword interface name can be user defined
name the default signature of variable is public static final and for method is
public abstract. JVM will be added implicitly public static final
303
before data members and public abstract before method.
INTERFACE IN JAVA

Example
public static final datatype variable name=value; ----> for data member
public abstract returntype methodname(parameters)---> for method
Implementing Interfaces:
A class uses the implements keyword to implement an interface. The
implements keyword appears in the class declaration following the extends
portion of the declaration.
Example
interface Person {
void run();
}
class Employee implements Person
{ public void run() {
304
System.out.println("Run fast"); } }
INTERFACE IN JAVA

INTERFACE IN JAVA
When we use abstract and when Interface
• If we do not know about any things about implementation just we have
requirement specification then we should be go for Interface
• If we are talking about implementation but not completely (partially
implemented) then we should be go for abstract
Rules for implementation interface
• A class can implement more than one interface at a time.
• A class can extend only one class, but implement many interfaces.
• An interface can extend another interface, similarly to the way that a class
can extend another class.
Relationship between class and Interface
• Any class can extends another class
305

306
• Any class can Implements another Interface
• Any Interface can not extend or Implements any class.
INTERFACE IN JAVA
• Any Interface can extends another Interface.

307
Abstract class Interface
1
It is collection of abstract method and
concrete methods.
It is collection of abstract method.
2
There properties can be reused
commonly in a specific application.
There properties commonly usable in
any application of java environment.
3 It does not support multiple inheritance. It support multiple inheritance.
4
Abstract class is preceded by abstract
keyword.
It is preceded by Interface keyword.
5
Which may contain either variable or
constants.
Which should contains only constants.
6
The default access specifier of abstract
class methods are default.
There default access specifies of
interface method are public.
INTERFACE IN JAVA
Difference between Abstract class and Interface

308
Abstract class Interface
7
These class properties can be reused
in other class using extend keyword.
These properties can be reused in any
other class using implements keyword.
8
Inside abstract class we can take
constructor.
Inside interface we can not take any
constructor.
9
For the abstract class there is no
restriction like initialization of
variable at the time of variable
declaration.
For the interface it should be compulsory
to initialization of variable at the time of
variable declaration.
10
There are no any restriction for
abstract class variable.
For the interface variable can not declare
variable as private, protected, transient,
volatile.
11
There are no any restriction for
abstract class method modifier that
means we can use any modifiers.
For the interface method can not declare
method as strictfp, protected, static,
native, private, final, synchronized.
INTERFACE IN JAVA

// abstract method
309
Run fast
Example of Interface
interface Person
{ void run();
}
class A implements Person
{ public void run()
{ System.out.println("Run
fast");
}
{ A obj = new A();
obj.run();
} }
Output
INTERFACE IN JAVA

INTERFACE IN JAVA
Multiple Inheritance using interface
Example
interface Developer
{ void disp();
}
interface Manager {
void show();
}
class Employee implements Developer, Manager
{ public void disp() {
System.out.println("Hello Good Morning");
}
public void show() {
310

}
{
obj.disp();
obj.show();
}
}
311
Output
Hello Good Morning
How are you ?
INTERFACE IN JAVA

INTERFACE IN JAVA
Marker or tagged interface
An interface that have no member is known as marker or tagged interface. For
example: Serializable, Cloneable, Remote etc. They are used to provide some
essential information to the JVM so that JVM may perform some useful
operation.
Example
public interface Serializable
{
……
}
//Way of writing Serializable interface
312

INTERFACE IN JAVA
Why interface have no constructor ?
• Because, constructor are used for eliminate the default values by user
defined values, but in case of interface all the data members are public
static final that means all are constant so no need to eliminate these values.
• Other reason because constructor is like a method and it is concrete method
and interface does not have concrete method it have only abstract methods
that's why interface have no constructor.
313

ABSTRACTION IN JAVA
Abstraction is the concept of exposing only the required essential
characteristics and behavior with respect to a context.
Hiding of data is known as data abstraction. In object oriented
programming language this is implemented automatically while writing the
code in the form of class and object.
Real Life Example of Abstraction in Java
Abstraction shows only important things to the user and hides the internal
details, for example, when we ride a bike, we only know about how to ride bikes
but can not know about how it work? And also we do not know the internal
functionality of a bike.
31 4

Note: Data abstraction can be used to provide security for the data from the
unauthorized methods.
Note: In Java language data abstraction can achieve using class.
ABSTRACTION IN JAVA
Another real life example of Abstraction is ATM Machine; All are performing
operations on the ATM machine like cash withdrawal, money transfer, retrieve
mini-statement…etc. but we can't know internal details about ATM.
315

Example of Abstraction
class Customer
{ int account_no;
float balance_Amt;
String name;
int age;
String address;
void
balance_inquiry()
{
/* to perform balance inquiry only account number is required that means
remaining properties are hidden for balance inquiry method */ }
void fund_Transfer() {
/* To transfer the fund account number and balance is required and
remaining properties are hidden for fund transfer method */ }
316
ABSTRACTION IN JAVA

ABSTRACTION IN JAVA
How to achieve Abstraction ?
There are two ways to achieve abstraction in java
• Abstract class (0 to 100%)
• Interface (Achieve 100% abstraction)
Read more about Interface and Abstract class in the previous section.
Difference between Encapsulation and Abstraction
Encapsulation is not providing full security because we can access private
member of the class using reflection API, but in case of Abstraction we can't
access static, abstract data member of a class.
317

ENCAPSULATION IN JAVA
Encapsulation is a process of wrapping of data and methods in a single unit is
called encapsulation. Encapsulation is achieved in java language by class
concept.
Combining of state and behavior in a single container is known as
encapsulation. In java language encapsulation can be achieve using class
keyword, state represents declaration of variables on attributes and behavior
represents operations in terms of method.
Advantage of Encapsulation
The main advantage of using of encapsulation is to secure the data from other
methods, when we make a data private then these data only use within the
class, but these data not accessible outside the class.
Real life example of Encapsulation in Java
The common example of encapsulation is capsule. In capsule all medicine
318
are encapsulated in side capsule.

Benefits of encapsulation
• Provides abstraction between an object and its clients.
• Protects an object from unwanted access by clients.
• Example: A bank application forbids (restrict) a client to change an
319
Account's balance.

Let's see the Example of Encapsulation in java
class Employee
{
private String name;
public String getName()
{
return name;
}
public void setName(String name)
{
this.name=name;
}
}
320

class Demo
{
{
Employee e=new Employee();
e.setName("Harry");
System.out.println(e.getName());
}
}
Output
Harry
321

POLYMORPHISM IN JAVA
The process of representing one form in multiple forms is known as
Polymorphism.
Polymorphism is derived from 2 greek words: poly and morphs.
The word "poly" means many and "morphs" means forms. So
polymorphism means many forms.
Polymorphism is not a programming concept but it is one of the principal of
OOPs. For many objects oriented programming language polymorphism
principle is common but whose implementations are varying from one objects
oriented programming language to another object oriented programming
language.
322

Real life example of polymorphism
Suppose if you are in class room that time you behave like a student, when you
are in market at that time you behave like a customer, when you at your home
at that time you behave like a son or daughter, Here one person present in
different-different behaviors.
323

How to achieve Polymorphism in Java ?
In java programming the Polymorphism principal is implemented with
method overriding concept of java.
Polymorphism principal is divided into two sub principal they are:
• Static or Compile time polymorphism
• Dynamic or Runtime polymorphism
Note: Java programming does not support static polymorphism because of its
limitations and java always supports dynamic polymorphism.
Let us consider the following diagram
Here original form or original method always resides in base class and multiple
forms represents overridden method which resides in derived
classes.
324

In the above diagram the
sum method which is present
in BC class is called original
form and the sum() method
which are present in DC1 and
DC2 are called overridden
form hence Sum() method is
originally available in only
one form
325
and it
implemented
is
further in
multiple
forms. Hence Sum() method
is one of the polymorphism
method.

So it is known as runtime
326
}
determined by the JVM not compiler,
polymorphism.
Example of Polymorphism in Java
class Person {
void walk() {
System.out.pri
ntln("Can
Run....");
}
Example of Runtime Polymorphism in Java
In below example we create two class Person an Employee, Employee class
extends Person class feature and override walk() method. We are calling the
walk() method by the reference variable of Parent class. Since it refers to the
subclass object and subclass method overrides the Parent class method,
subclass method is invoked at runtime. Here method invocation is

Output
Running fast...
327
class Employee extends Person
{ void walk() {
System.out.println("Running
Fast...");
}
public static void main(String arg[])
{ Person p=new Employee();
//upcasting p.walk();
}
}

Dynamic Binding
Dynamic binding always says create an object of base class but do not create
the object of derived classes. Dynamic binding principal is always used for
executing polymorphic applications.
The process of binding appropriate versions (overridden method) of derived
classes which are inherited from base class with base class object is known as
dynamic binding.
Advantages of dynamic binding along with polymorphism with method
overriding are.
• Less memory space
• Less execution time
• More performance
328

Static polymorphism
The process of binding the overloaded method within object at compile time is
known as Static polymorphism due to static polymorphism utilization of
resources (main memory space) is poor because for each and every overloaded
method a memory space is created at compile time when it binds with an object.
In C++ environment the above problem can be solve by using dynamic
polymorphism by implementing with virtual and pure virtual function so most
of the C++ developer in real worlds follows only dynamic polymorphism.
Dynamic polymorphism
In dynamic polymorphism method of the program binds with an object at
runtime the advantage of dynamic polymorphism is allocating the memory
space for the method (either for overloaded method or for override method)
329
at run time.

Conclusion
The advantage of dynamic polymorphism is effective utilization of the
resources, So Java always use dynamic polymorphism. Java does not support
static polymorphism because of its limitation.
330

Package in Java
A package is a collection of similar types of classes, interfaces and sub-
packages.
Purpose of package
The purpose of package concept is to provide common classes and
interfaces for any program separately. In other words if we want to develop
any class or interface which is common for most of the java programs than
such common classes and interfaces must be place in a package.
PACKAGE IN JAVA
331

PACKAGE IN JAVA
Packages in Java are the way to organize files when a project has many
modules. Same like we organized our files in Computer. For example we store all
movies in one folder and songs in other folder, here also we store same type of
files in a particular package for example in awt package have all classes and
interfaces for design GUI components.
332

Advantage of package
Package is used to categorize the classes and interfaces so that they can be
easily maintained
• Application development time is less, because reuse the code
• Application memory space is less (main memory)
• Application execution time is less
• Application performance is enhance (improve)
• Redundancy (repetition) of code is minimized
• Package provides access protection.
• Package removes naming collision.
Type of package
Package are classified into two type which are given below.
• Predefined or built-in package
333
• User defined package
PACKAGE IN JAVA

Predefined or built-in package
These are the package which are already designed by the Sun Microsystem
and supply as a part of java API, every predefined package is collection of
predefined classes, interfaces and sub-package.
User defined package
If any package is design by the user is known as user defined package. User
defined package are those which are developed by java programmer and supply
as a part of their project to deal with common requirement.
Rules to create user defined package
• package statement should be the first statement of any package program.
• Choose an appropriate class name or interface name and whose modifier
must be public.
• Any package program can contain only one public class or only one public
interface but it can contain any number of normal classes. 334
PACKAGE IN JAVA

• Package program should not contain any main class (that means it should
not contain any main())
• modifier of constructor of the class which is present in the package must be
public. (This is not applicable in case of interface because interface
have no constructor.)
• The modifier of method of class or interface which is present in the package
must be public (This rule is optional in case of interface because interface
methods by default public)
• Every package program should be save either with public class name or
public Interface name
335
PACKAGE IN JAVA

PACKAGE IN JAVA
336

Compile package programs
For compilation of package program first we save program with public
className.java and it compile using below syntax:
Syntax
javac -d . className.java
Syntax
javac -d path className.java
Explanations: In above syntax "-d" is a specific tool which is tell to java
compiler create a separate folder for the given package in given path. When we
give specific path then it create a new folder at that location and when we use .
(dot) then it crate a folder at current working directory.
Note: Any package program can be compile but can not be execute or run.
These program can be executed through user defined program which are
importing package program. 337
PACKAGE IN JAVA

PACKAGE IN JAVA
Example of package program
Package program which is save with A.java and compile by javac -d . A.java
Example
package mypack;
public class A
{
public void show()
{
System.out.println("Sum method");
}
}
Import above class in below program using import
packageName.className
338

Example
import mypack.A;
public class Hello
{
public static void
main(String
arg[])
{
A a=new A();
a.show();
System.out.pr
intln("show()
class A");
}
}
Explanation
s: In the
339
import class "
A"in class Hello using "import mypack.A;" statement.
PACKAGE IN JAVA

PACKAGE IN JAVA
Difference between Inheritance and package
• Inheritance concept always used to reuse the feature within the program
between class to class, interface to interface and interface to class but not
accessing the feature across the program.
• Package concept is to reuse the feature both within the program and across
the programs between class to class, interface to interface and interface to
class.
Difference between package keyword and import keyword
• Package keyword is always used for creating the undefined package and
placing common classes and interfaces.
• import is a keyword which is used for referring or using the classes and
interfaces of a specific package.
340

EXCEPTION HANDLING IN JAVA
The process of converting system error messages into user friendly error
message is known as Exception handling. This is one of the powerful feature
of Java to handle run time error and maintain normal flow of java application.
Exception
An Exception is an event, which occurs during the execution of a program,
that disrupts the normal flow of the program's Instructions.
Why use Exception Handling
Handling the exception is nothing but converting system error generated
message into user friendly error message. Whenever an exception occurs in the
java application, JVM will create an object of appropriate exception of sub class
and generates system error message, these system generated messages are not
understandable by user so need to convert it into user
341
friendly error message.

You can convert system error message into user friendly error message by
using exception handling feature of java.
For Example: when you divide any number by zero then system generate / by
zero
so this is not understandable by user so you can convert this message into user
friendly error message like Don't enter zero for denominator.
342

Hierarchy of Exception classes
343

Type of Exception
• Checked Exception
• Un-Checked Exception
Checked Exception
Checked Exception are the exception which checked at compile-time.
These exception are directly sub-class of java.lang.Exception class.
Only for remember: Checked means checked by compiler so checked
exception are checked at compile-time.
344

Un-Checked Exception
Un-Checked Exception are the exception both identifies or raised at run time.
These exception are directly sub-class of java.lang.RuntimeException class.
Note: In real time application mostly we can handle un-checked exception.
Only for remember: Un-checked means not checked by compiler so un-
checked exception are checked at run-time not compile time.
345

Checked Exception Un-Checked Exception
1
checked Exception are checked
at compile time
un-checked Exception are checked at run time
2
e.g. FileNotFoundException,
NumberNotFoundException etc.
e.g. ArithmeticException,
NullPointerException,
ArrayIndexOutOfBoundsException etc.
346
Difference between Error and Exception
Error Exception
1 Can't be handle. Can be handle.
2
Example:
NoSuchMethodError
OutOfMemoryError
Example:
ClassNotFoundException
NumberFormateException
Difference between checked Exception and un-checked Exception

Handling the Exception
Handling the exception is nothing but converting system error generated
message into user friendly error message in others word whenever an
exception occurs in the java application, JVM will create an object of
appropriate exception of sub class and generates system error message, these
system generated messages are not understandable by user so need to convert
it into user-friendly error message. You can convert system error message into
user-friendly error message by using exception handling feature of java.
Use Five keywords for Handling the Exception
• try
• catch
• finally
• throws
• throw
347

Syntax for handling the exception
Syntax
Try {
//
state
ment
s
cause
s
probl
em at
run
time
}
catch(
type of
excepti
on-1
object-
1) {
// statements which will execute compulsory
}
348

Example without Exception Handling
Syntax
class ExceptionDemo
{
{
int a=10, ans=0;
ans=a/0;
System.out.printl
n("Denominator
not be zero");
}
}
Abnormally terminate program and give a message like below, this error
message is not understandable by user so we convert this error message
349
into user friendly error message, like "denominator not be zero".

Example of Exception Handling
class ExceptionDemo {
{ int a=10, ans=0;
Try {
ans=a/0;
}
catch (Exception e)
{ System.out.println("Denominator not be zero");
}
}
}
Output
350
Denominator not be zero

try block
Inside try block we write the block of statements which causes executions
block always contains problematic
at run time in other words try
statements.
Important points about try block
• If any exception occurs in try block then CPU controls comes out to the try
block and executes appropriate catch block.
• After executing appropriate catch block, even through we use run time
statement, CPU control never goes to try block to execute the rest of the
statements.
• Each and every try block must be immediately followed by catch block that
is no intermediate statements are allowed between try and catch block.
351

Syntax
Try {
.....
}
/* Here no other statements are allowed
between try and catch block */
catch() {
....
}
• Each and every try block must contains at least one catch block. But it is
highly recommended to write multiple catch blocks for
generating
multiple user friendly error messages.
• One try block can contains another try block that is nested or inner try
352
block can be possible.

Syntax
Try { .......
Try { ....... } }
catch block
• Inside catch block we write the block of statements which will generates
user friendly error messages.
• catch block important points
• catch block will execute exception occurs in try block.
• You can write multiple catch blocks for generating multiple user friendly
error messages to make your application strong. You can see below example.
• At a time only one catch block will execute out of multiple catch blocks.
• in catch block you declare an object of sub class and it will be internally
353
referenced by JVM.

Multiple catch block
You can write multiple catch blocks for generating multiple user friendly error
messages to make your application strong. You can see below example.
Example
import java.util.*; class
ExceptionDemo {
{ int a, b, ans=0;
System.out.println("Enter any two numbers: ");
try {
a=s.nextInt();
354
b=s.nextInt();

ans=a/b;
System.out.println("Result: "+ans); }
catch(ArithmeticException ae)
}
catch(Exception e)
{ System.out.println("Enter valid number");
}
}
}
Output
Enter any two number: 5 0
355

356
finally Block in Exception Handling
Inside finally block we write the block of statements which will relinquish
(released or close or terminate) the resource (file or database) where data store
permanently.
finally block important points
• Finally block will execute compulsory
• Writing finally block is optional.
• You can write finally block for the entire java program
• In some of the circumstances one can also write try and catch block in finally
block.

357
Example
{ int a=10, ans=0;
Try {
ans=a/0;
}
catch (Exception e)
}
Finally {
System.out.println("I am from finally block");
}
} }
Output
I am from finally block

358
• ClassNotFoundException
• IOException
• InterruptedException
Un-Checked Exception Classes
• ArithmeticException
• ArrayIndexOutOfBoundsException
• StringIndexOutOfBoundsException
• NumberFormateException
• NullPointerException
• NoSuchMethodException
• NoSuchFieldException
Exception Classes in Java
Exception are mainly classified into two type checked exception and un-
checked exception.
Checked Exception Classes
• FileNotFoundException

FileNotFoundException
If the given filename is not available in a specific location ( in file handling
concept) then FileNotFoundException will be raised. This exception will be
thrown by the FileInputStream, FileOutputStream, and RandomAccessFile
constructors.
ClassNotFoundException
If the given class name is not existing at the time of compilation or running of
program then ClassNotFoundException will be raised. In other words this
exception is occured when an application tries to load a class but no definition
for the specified class name could be found.
359

IOException
This is exception is raised whenever problem occurred while writing and
reading the data in the file. This exception is occurred due to following reason;
• When try to transfer more data but less data are present.
• When try to read data which is corrupted.
• When try to write on file but file is read only.
InterruptedException
This exception is raised whenever one thread is disturb the other thread. In
other words this exception is thrown when a thread is waiting, sleeping, or
otherwise occupied, and the thread is interrupted, either before or during the
activity.
369

ArithmeticException
This exception is raised because of problem in arithmetic operation like divide
by zero. In other words this exception is thrown when an exceptional
arithmetic condition has occurred. For example, an integer "divide by zero".
Example
{ int a=10, ans=0;
Try
{ ans=a/
0;
}
catch
(Exceptio
n e) {
System.o
361
} } }

ArrayIndexOutOfBoundsException
This exception will be raised whenever given index value of an array is out of
range. The index is either negative or greater than or equal to the size of the
array.
Example
int a[]=new int[5];
a[10]=100; //ArrayIndexOutOfBoundsException
362

StringIndexOutOfBoundsException
This exception will be raised whenever given index value of string is out of
range. The index is either negative or greater than or equal to the size of the
array.
Example
String s="Hello";
s.charAt(3);
s.charAt(10);
// Exception raised chatAt() is a predefined method of string class used to get
the individual characters based on index value.
363

NumberFormateException
This exception will be raised whenever you trying to store any input value in
the un-authorized datatype.
Example: Storing string value into int datatype.
Example
int a;a="Hello";
Example
String s="hello"; int i=Integer.parseInt(s);//NumberFormatException
NoSuchMethodException
This exception will be raised whenever calling method is not existing in the
program.
364

Example
String s=null;
System.out.println(s.length());
365
//NullPointerException
StackOverFlowException
This exception throw when full the stack because the recursion method are
stored in stack area.
NullPointerException
A NullPointerException is thrown when an application is trying to use or
access an object whose reference equals to null.

Difference Between Throw and Throws Keyword
throw
throw is a keyword in java language which is used to throw any user defined
exception to the same signature of method in which the exception is raised.
Note: throw keyword always should exist within method body.
whenever method body contain throw keyword than the call method should be
followed by throws keyword.
366

Syntax
class className
{
returntype method(...) throws Exception_class
{
throw(Exception obj)
}
}
367

throws
throws is a keyword in java language which is used to throw the exception
which is raised in the called method to it's calling method throws keyword
always followed by method signature.
Example
returnType methodName(parameter)throws Exception_class....
{
.....
}
368

throw throws
1
throw is a keyword used for hitting and
generating the exception which are
occurring as a part of method body
throws is a keyword which gives an indication
to the specific method to place the common
exception methods as a part of try and catch
block for generating user friendly error
messages
2
The place of using throw keyword is
always as a part of method body.
The place of using throws is a keyword is
always as a part of method heading
3
When we use throw keyword as a part
of method body, it is mandatory to the
java programmer to write throws
keyword as a part of method heading
When we write throws keyword as a part of
method heading, it is optional to the java
programmer to write throw keyword as a part
of method body.
369
Difference between throw and throws

Example of throw and throws
// save by DivZero.java
package pack;
public class DivZero {
public void division(int
a, int b)throws
ArithmeticException {
if(b==0) {
ArithmeticException ae=new ArithmeticException("Does not enter zero for
Denominator");
throw ae;
}
else {
int c=a/b;
System.out.println("Result: "+c);
370
} } } Compile: javac -d . DivZero.java

Example
// save by ArthException.java
import pack.DivZero;
import java.util.*;
class ArthException
{
args[])
{
System.out.println("Enter any two number: ");
try
{
int a=s.nextInt(); 371
int b=s.nextInt();

DivZero dz=new DivZero();
dz.division(a, b);
}
catch(Exception e)
{
System.err.println(e);
}
}
}
372

Steps to Compile and Run code
First you save throw-example files into you PC in any where, here i will save
this file in C:>
C:throw-example>javac -d . DivZero.java C:
throw-example>javac ArthException.java
Note: First compile DivZero.java code then compile ArthException.java3co7d3e.
Compile: javac ArthException.java

Custom Exception in Java
If any exception is design by the user known as user defined or Custom
Exception. Custom Exception is created by user.
Rules to design user defined Exception
• Create a package with valid user defined name.
• Create any user defined class.
• Make that user defined class as derived class of Exception
or RuntimeException class.
• Declare parameterized constructor with string variable.
• call super class constructor by passing string variable within the derived class
constructor.
• Save the program with public class name.java
374

Example
// save by AgeException.java
package nage;
public class AgeException extends Exception
{ public AgeException(String s) {
super(s);
375
} }

Compile: javac -d . AgeException.java
Example : // save by CheckAge.java
package nage;
public class CheckAge {
public void verify(int age)throws
AgeException {
if (age>0)
{ System.err.print("valid
age");
}
Else {
AgeException ae=new AgeException("Invalid age");
throw(ae);
}
}
376
}

Compile: javac -d . CheckAge.java
Example :
// save by VerifyAgeException
import nage.AgeException;
import nage.CheckAge;
import java.util.*;
public class VerifyAgeException
{
args[])
{
int a;
System.out.println("Enter your
age");
Scanner s=new
Scanner(System.in);
377
a=s.nextInt();

try
{
CheckAge ca=new CheckAge();
ca.verify(a);
}
catch(AgeException ae)
{
Syso("Age should not be -ve");
}
catch(Exception e)
{ System.err.println(e
);
}
} 378
}

Steps to compile and run above program
First you save verify-age files into you PC in any where, here i will save this file in
C:>
C:verify-age>javac -d . AgeException.java
C:verify-age>javac -d . CheckAge.java
C:verify-age>javac VerifyAgeException.java
Note: First compile AgeException.java code
then CheckAge.java and at last 379
compile VerifyAgeException.java code.
Compile: javac VerifyAgeException.java

MULTITHREADING IN JAVA
Multithreading in java is a process of executing multiple threads
simultaneously. The aim of multithreading is to achieve the concurrent
execution.
Thread
Thread is a lightweight components and it is a flow of control. In other
words a flow of control is known as thread.
State or Life cycle of thread
State of a thread are classified into five types they are
• New State
• Ready State
• Running State
• Waiting State
• Halted or dead State
380

New State
If any new thread class is created that represent new state of a thread, In new
state thread is created and about to enter into main memory. No memory is
available if the thread is in new state.
Ready State
In ready state thread will be entered into main memory, memory space is
allocated for the thread and 1st time waiting for the CPU.
Running State
381
Whenever the thread is under execution known as running state.

Halted or dead State
If the thread execution is stopped permanently than it comes under dead state,
no memory is available for the thread if its comes to dead state.
Note: If the thread is in new or dead state no memory is available but
sufficient memory is available if that is in ready or running or waiting state.
Achieve multithreading in java
In java language multithreading can be achieve in two different ways.
• Using thread class
• Using Runnable interface
382

Using thread class
• In java language multithreading program can be created by following below
rules.
• Create any user defined class and make that one as a derived class of
thread class.
class Class_Name extends Thread{........}
• Override run() method of Thread class (It contains the logic of perform any
operation)
• Create an object for user-defined thread class and attached that object to
predefined thread class object.
Class_Name obj=new Class_Name
Thread t=new Thread(obj);
• Call start() method of thread class to execute run() method.
383
• Save the program with filename.java

384

Example of multithreading using Thread class
Thread based program for displaying 1 to 10 numbers after each and every
second.
// Threaddemo2.java
class Th1 extends Thread
{
public void run()
{
try
{
for(int i=1;i< =10;i++)
{
System.out.println("value of i="+i);
385
Thread.sleep(1000);

}
}
catch(InterruptedException ie)
{
System.err.println("Problem in thread execution");
}
}
}
class Threaddemo2
{
{
Th1 t1=new Th1();
386
System.out.println("Execution status of t1 before start="+t1.isAlive());

t1.start();
System.out.println("Execution status of t1 before start="+t1.isAlive());
try
{
Thread.sleep(5000);
}
{
System.out.println("Problem in thread execution");
}
System.out.println("Execution status of t1 during
execution="+t1.isAlive());
Try
{ 387
Thread.sleep(5001);

}
{
System.out.println("problem in thread execution");
}
System.out.println("Execution status of t1 after completation="+t1.isAlive());
}
}
388

Output
Execution status of t1 before start=false //new state
10 Execution status of t1 after completion=false //halted state
389
//ready state
Execution status of t1 after start=true
1
2
3
4
5
//running state
6 Execution status of t1 during execution=true 7
8
9

Thread class properties
Thread class contains constant data members, constructors, predefined
methods.
Constant data members
• MAX-PRIORITY
• MIN-PRIORITY
• NORM-PRIORITY
MAX-PRIORITY
Which represent the minimum priority that a thread can have whose values is
10.
Syntax: public static final int MAX-PRIORITY=10
MIN-PRIORITY
Which represents the minimum priority that a thread can have.
390
Syntax: public static final int MIN-PRIORITY=0

NORM-PRIORITY
Which represent the default priority that is assigned to a thread.
Syntax: public static final int NORM-PRIORITY=5
Constructors of Thread class
• Thread()
• Thread(String name)
• Thread(object)
• Thread(object, String name)
Thread()
Which will be execute to set the predefined name for newly created thread,
these names are generally in the form of thread -0, thread -1,
....
Syntax to call constructor:
Syntax 391
Thread t=new Thread();

Thread(String name)
Which can be used to provide user defined name for newly created thread.
Syntax : Thread t=new Thread("newthread");
Thread(object)
Which can be used to provide default name for newly created user defined
thread.
Syntax : UserdefinedThreadclass obj=new UserdefinedThreadclass();
Thread t=new Thread("obj");
Thread(object, String name)
Which will be used to provide user defined name for the newly created user
defined thread.
Syntax : UserdefinedThreadclass obj=new UserdefinedThreadclass();
Thread t=new Thread(object, "secondthread");
392

• getPriority()
• setPriority()
• getName()
• setName()
• isDeamon()
• run()
• start()
• sleep()
393
• suspend()
• resume()
• stop()
• isAlive()
• currentThread()
• join()
• getState()
• yield()
Methods of Thread class

getPriority()
This method is used to get the current priority of thread.
int x=t.getPriority();
System.out.println(x);
setPriority()
This method is used to
set the current priority
of thread.
t.setPriority(any priority number between o to 10)
or
t.setPriority(Thread.MAX-PRIORITY)
394

getName()
This method is used to get the current executing thread name.
String s=t.getName();
System.out.println(s);
setName()
This method is used to
set the userdefined
name for the thread.
t.setName("mythread");
isDeamon()
Which returns true if
the current thread is
background thread
otherwise
return false.
395
boolean b=t.isDeamon();

run()
Which contains the main business logic that can be executed by multiple
threads simultaneously in every user defined thread class run method
should be overridden.
public Class_Name extends Thread
{
public void run() {
.....
}
}
start()
Used to convert ready state thread to running state.
396
t.start();

sleep()
Used to change running state thread to ready state based on time period it is a
static method should be called with class reference.
public static final sleep(long milisecond)throws InterruptedException
{
try
{ Thread.sleep(3000)
;
}
catch(InterruptedEx
ception ie)
{ ........
}
}
Once the given time
period is completed
thread state
397
from waiting to running state.

suspend()
Used to convert running state thread to waiting state, which will never come
back to running state automatically.
t.suspend();
resume()
Used to change the suspended thread state(waiting state) to ready state.
t.resume();
Note: Without using
suspend() method
resume() method can
not be use.
398

What is the difference between sleep() and suspend()
• Sleep() can be used to convert running state to waiting state and
automatically thread convert from waiting state to running state once the
given time period is completed.
• Where as suspend() can be used to convert running state thread to
waiting state but it will never return back to running state automatically.
stop()
This method is used to convert running state thread to dead state.
t.stop();
isAlive()
Which is return true if
the thread is in ready or
running or waiting state
and return false if the
thread is in new or dead
state.
399
Thread t=new Thread(); t.isAlive();

currentThread()
Used to get the current thread detail like thread name thread group name and
priority
t.currentThread();
Note: The default thread name is thread-0,
(if it is a main thread default name is main)
The default thread group name is main
Default thread priority is "5" is normal
priority.
join()
Which can be used to combined more than
one thread into a single group
400
signature is public final void join()throws InterruptedException

try
{
t.join();
t2.join();
.....
}
getState()
This method is used to get the current state of thread.
t.getState();
yield()
Which will keep the
currently executing
thread into temporarily
pass and
allows other threads to
execute
401

Using Runnable Interface
• Runnable is one of the predefined interface in java.lang package, which is
containing only one method and whose prototype is " Public abstract void
run "
• The run() method of thread class defined with null body and run() method
of Runnable interface belongs to abstract. Industry is highly recommended
to override abstract run() method of Runnable interface but not
recommended to override null body run() method of thread class.
• In some of the circumstance if one derived class is extending some type of
predefined class along with thread class which is not possible because
java programming never supports multiple inheritance. To avoid this
multiple inheritance problem, rather than extending thread class we
402
implement Runnable interface.

403
class Class_Name implement Runnable
........
}
}
Class_Name obj=new Class_name();
Rules to create the thread using Runnable interface
• Create any user defined class and implements runnable interface within
that
• Override run() method within the user defined class.
• call start() method to execute run() method of thread class
• Save the program with classname.java
Note: While implementing runnable
interface it is very mandatory to
extending Thread class.
t.start();
attach user defined thread class
object reference to predefined
thread class object reference. It is
optional while creating thread by

Thread Synchronization
Whenever multiple threads are trying to use same resource than they may be
chance to of getting wrong output, to overcome this problem thread
synchronization can be used.
Definition: Allowing only one thread at a time to utilized the same resource
out of multiple threads is known as thread synchronization or thread safe.
In java language thread synchronization can be achieve in two different ways.
• Synchronized block
• Synchronized method
Note: synchronization is a keyword (access modifier in java)
404

Synchronized block
Whenever we want to execute one or more than one statement by a single
thread at a time(not allowing other thread until thread one execution is
completed) than those statement should be placed in side synchronized
block.
class Class_Name implement Runnable or extends Thread
synchronized(this) {
.......
.......
}
}
}
405

Synchronized method
Whenever we want to allow only one thread at a time among multiple thread
for execution of a method than that should be declared as synchronized
method.
class Class_Name implement Runnable or extends Thread {
public void run()
{ synchronized void fun()
{
.......
.......
}
public void run() {
fun();
.... 406
} }

Interthread Communication
The process of execution of exchanging of the data / information between
multiple threads is known as Interthread communication or if an output of
first thread giving as an input to second thread the output of second thread
giving as an input to third thread then the communication between first
second and third thread known as Interthread communication.
In order to develop Interthread communication application we use some of the
methods of java.lang.Object class and these methods are known as Interthread
communication methods.
Interthread communication methods
• public final void wait(long msec)
• public final void wait()
• public final void notify()
407
• public final void notifyAll()

public final void wait(long msec)
public final void wait (long msec) is used for making the thread to wait by
specifying the waiting time in terms of milliseconds. Once the waiting time is
completed, automatically the thread will be interred into ready state from
waiting state.
This methods is not recommended to used to make next thread to wait on the
basis of time because java programmer may not be able to decide or determine
the CPU burst time of current thread and CPU burst time is decided by OS but
not by the programmer.
public final void wait()
public final void wait() is used for making the thread to wait without
specifying any waiting time this method is recommended to use to make
the next thread to wait until current thread complete its execution.
408

public final void notify()
public final void notify() is used for transferring one thread at a time from
waiting state to ready state.
public final void notifyAll()
public final void notifyAll() is used for transferring all the threads at a time
from waiting state to ready state.
Note: public final void wait (long msec) and public final void wait() throws a
predefined Exception called java.lang.InterruptedException.
409

STRING HANDLING IN JAVA
String Handling in Java
• The basic aim of String Handling concept is storing the string data in the
main memory (RAM), manipulating the data of the String, retrieving the
part of the String etc.
• String Handling provides a lot of concepts that can be performed on a
string such as concatenation of string, comparison of string, find sub string
etc.
Character
It is an identifier enclosed within single quotes (' ').
Example: 'A', '$', 'p'
String:
String is a sequence of characters enclosed within double quotes (" ") is
known as String.
410
Example: "Java Programming".

In java programming to store the character data we have a fundamental
datatype called char. Similarly to store the string data and to perform various
operation on String data, we have three predefined classes they are:
• String
• StringBuffer
• StringBuilder
String class
• It is a predefined class in java.lang package can be used to handle the String.
String class is immutable that means whose content can not be changed at
the time of execution of program.
• String class object is immutable that means when we create an object of
String class it never changes in the existing object.
411

Example
class StringHandling
{
{
String s=new String("java");
s.concat("software");
}
}
Output
java
Explanation: Here we can
not change the object of
String class so output is
412
only java not java software.

Methods of String class
length()
length(): This method is
used to get the number of
character of any string.
Example
class StringHandling {
{ int l;
String s=new String("Java");
l=s.length();
System.out.println("Length: "+l);
}
}
Output
413
Length: 4

charAt(index)
charAt(): This method is used to get the character at a given index value.
Example
{
char c;
String s=new String("Java");
c=s.charAt(2);
System.out.println("Character: "+c);
}
}
Output
414
Character: v

toUpperCase()
toUpperCase(): This method is use to convert lower case string into upper case.
Example
{
{
String s="Java";
System.out.println("String: "+s.toUpperCase());
}
}
Output
415
String: JAVA

toLowerCase()
toLowerCase(): This method is used to convert lower case string into upper
case.
Example
{
{
String s="JAVA";
System.out.println("String: "+s.toLowerCase());
}
}
Output
416
String: java

concat()
concat(): This method is used to combined two string.
Example
{
{
String s1="Hitesh";
String s2="Raddy";
System.out.println(
"Combined String:
"+s1.concat(s2));
}
}
Output
417
Combined String: HiteshRaddy

equals()
equals(): This method is used to compare two strings, It return true if strings
are same otherwise return false. It is case sensitive method.
Example
{ String s1="Hitesh";
String s2="Raddy";
String s3="Hitesh";
System.out.println("Compare String: "+s1.equals(s2));
System.out.println("Compare String: "+s1.equals(s3)); } }
Output
Compare String: false
418
Compare String: true

equalsIgnoreCase()
equalsIgnoreCase(): This method is case insensitive method, It return true if
the contents of both strings are same otherwise false.
Example
String s2="HITESH";
String s3="Raddy";
System.out.println("Compare String: "+s1.equalsIgnoreCase(s2));
System.out.println("Compare String: "+s1.equalsIgnoreCase(s3)); } }
Output
419

compareTo()
compareTo(): This method is used to compare two strings by taking unicode
values, It return 0 if the string are same otherwise return +ve or - ve integer
values.
Example
System.out.println("Strings are same"); }
Else { System.out.println("Strings are not same"); } } }
420
String s2="Raddy";
int i;
i=s1.compareTo(s2);
if(i==0) {
Output
Strings are not same

String s1="Hitesh";
String s2="HITESH";
int i;
i=s1.compareToIgnoreCase(s2);
if(i==0) {
}
Else { System.out.println("Strings are not same"); } } }
421
System.out.println("Strings are same");
Output
Strings are same
compareToIgnoreCase()
compareToIgnoreCase(): This method is case insensitive method, which is used
to compare two strings similar to compareTo().
Example

startsWith()
startsWith(): This method return true if string is start with given another
string, otherwise it returns false.
Example
{
{
String s="Java is programming language";
System.out.println(s.startsWith("Java"));
}
}
Output
422
true

423
true
endsWith()
endsWith(): This method return true if string is end with given another string,
otherwise it returns false.
Example
{
{
System.out.println(s.endsWith("language"));
}
}
Output

subString()
subString(): This method is used to get the part of given string.
Example
{
{
System.out.println(s.substring(8)); // 8 is starting index
}
}
Output
programming language
424

Example
{
{
System.out.println(s.substring(8, 12));
}
}
Output
prog
425

indexOf()
indexOf(): This method is used find the index value of given string. It always
gives starting index value of first occurrence of string.
Example
{
{
System.out.println(s.indexOf("programming"));
}
}
Output
8
426

lastIndexOf()
lastIndexOf(): This method used to return the starting index value of last
occurence of the given string.
Example
public static void main(String arg[]) { String
s1="Java is programming language";
String s2="Java is good programming language";
System.out.println(s1.lastIndexOf("programming"));
System.out.println(s2.lastIndexOf("programming"));
} }
Output
8
13
427

trim()
trim(): This method remove space which are available before starting of
string and after ending of string.
Example
{
{
String s=" Java is programming language ";
System.out.println(s.trim());
}
}
Output
428
Java is programming language

split()
split(): This method is used to divide the given string into number of parts
based on delimiter (special symbols like @ space , ).
Example
{ String s="contact@tutorial4us.com";
String[] s1=s.split("@"); // divide string based on @
for(String c:s1) // foreach loop
{
System.out.println(c); } } }
Output
contact
429
@tutorial4us.com

replace()
replace(): This method is used to return a duplicate string by replacing old
character with new character.
Note: In this method data of original string will never be modify.
Example
{ String s1="java";
String s2=s1.replace('j', 'k');
System.out.println(s2);
}
}
Output
430
kava

StringBuffer Class in Java
• It is a predefined class in java.lang package can be used to handle the String,
whose object is mutable that means content can be modify.
• StringBuffer class is working with thread safe mechanism that means
multiple thread are not allowed simultaneously to perform operation of
StringBuffer.
• StringBuffer class object is mutable that means when we create an object of
StringBulder class it can be change.
Explanation: Here we can changes in the existing object of StringBuffer class
so output is javasoftware.
431

Example StringBuffer
{
{
StringBuffer sb=new StringBuffer("java");
sb.append("software");
System.out.println(sb);
}
}
Output
javasoftware
432

String StringBuffer
The data which enclosed within double
quote (" ") is by default treated as String
class.
The data which enclosed within double
quote (" ") is not by default treated as
StringBuffer class
String class object is immutable StringBuffer class object is mutable
When we create an object of String class
by default no additional character
memory space is created.
When we create an object of StringBuffer
class by default we get 16 additional
character memory space.
433
• We can not override the method of String and StringBuffer.
Similarities Between String and StringBuffer
• Both of them are belongs to public final. so that they never participates
in inheritance that is is-A relationship is not possible but they can always
participates in As-A and Uses-A relationship.
Difference Between String and StringBuffer

Methods of StringBuffer class
reverse()
reverse(): This method is used to reverse the given string and also the new
value is replaced by the old string.
Example
{
StringBuffer sb=new StringBuffer("java code");
System.out.println(sb.reverse());
}
}
Output
434
edoc avaj

insert()
insert(): This method is used to insert either string or character or integer or
real constant or boolean value at a specific index value of given string.
Example
{
{
StringBuffer sb=new StringBuffer("this is my java code");
System.out.println(sb.insert(11, "first "));
}
}
Output
435
this is my first java code

append()
append(): This method is used to add the new string at the end of original
string.
Example
{
{
StringBuffer sb=new StringBuffer("java is easy");
System.out.println(sb.append(" to learn"));
}
}
Output
436
java is easy to learn

replace()
replace() This method is used to replace any old string with new string based
on index value.
Example
StringBuffer sb=new StringBuffer("This is my code");
System.out.println(sb.replace(8, 10, "java"));
}
}
Output
This is java code
Explanation: In above example java string is
replaced with old string (my) 437
which is available between 8 to 10 index value.

deleteCharAt()
deleteCharAt(): This method is used to delete a character at given index
value.
Example
{
{
StringBuffer sb=new StringBuffer("java");
System.out.println(sb.deleteCharAt(3));
}
}
Output
438
jav

delete()
delete(): This method is used to delete string form given string based on index
value.
Example
StringBuffer sb=new StringBuffer("java is easy to learn");
StringBuffer s;
s=sb.delete(8, 13);
System.out.println(sb); } }
Output
java is to learn
Explanation: In above
example string will be
deleted which is existing
439
between 8 and 13 index value.

toString()
toString(): This method is used to convert mutable string value into
immutable string.
Example
{ StringBuffer sb=new StringBuffer("java");
String s=sb.toString();
s.concat("code");
}
}
Output
440
java

• By equals() method
• By == operator
• By compreTo() method
441
String Compare in Java
There are three way to compare string object in java:

equals() Method in Java
equals() method always used to comparing contents of both source and
destination String. It return true if both string are same in meaning and case
otherwise it returns false. It is case sensitive method.
442

Example
String s2="Raddy";
String s3="Hitesh";
}
}
Output
443

== or Double Equals to Operator in Java
== Operator is always used for comparing references of both source and
destination objects but not their contents.
444

Example
String s1=new String("java");
String s2=new String("java");
if(s1==s2) {
System.out.println("Strings are
same");
}
else {
System.out.println("Strings are
not same");
} } }
Output
445

compareTo() Method in Java
comapreTo() method can be used to compare two string by taking Unicode
values. It returns 0 if the string are same otherwise returns either +ve or - ve
integer.
Example
{
{
String s1="Hitesh";
String s2="Raddy";
int i;
i=s1.compareTo(s2);
446
if(i==0)

{
System.out.println("Strings are same");
}
else {
System.out.println("Strings are not same");
}
}
}
Output
447

Difference between equals() method and == operator
• equals() method always used to comparing contents of both source and
destination String.
• == Operator is always used for comparing references of both source and
destination objects but not their contents.
String Concatenation
There are two way to concat string object in java:
• By + (string concatenation) operator
• By concat() method
448

By + operator
Using Java string concatenation operator (+) you can combined two or
more strings.
Example
{
{
String s= "Java" + "Code";
}
}
Output
JavaCode
449

By concat() method
concat() method is used to combined two strings.
Example
String s1="Java";
String s2="Code";
String s3=s1.concat(s2);
System.out.println(s3);
}
}
Output
JavaCode
459

StringBuilder
• It is a predefined class in java.lang package can be used to handle the String.
StringBuilder class is almost similar to to StringBuffer class. It is also a
mutable object.
• The main difference StringBuffer and StringBuilder class is StringBuffer is
thread safe that means only one threads allowed at a time to work on the
String where as StringBuilder is not thread safe that means multiple threads
can work on same String value.
Difference between StringBuffer and StringBuilder
All the things between StringBuffer and StringBuilder are same only
difference is StringBuffer is synchronized and StringBuilder is not
synchronized. synchronized means one thread is allow at a time so it thread
safe. Not synchronized means multiple threads are allow at a time so it not
451
thread safe.

StringBuffer StringBuilder
1 It is thread safe. It is not thread safe.
2
Its methods are synchronized and
provide thread safety.
Its methods are not synchronized and
unable to provide thread safety.
3
Relatively performance is low because
thread need to wait until previous
process is complete.
Relatively performance is high because
no need to wait any thread it allows
multiple thread at a time.
4 Introduced in 1.0 version. Introduced in 1.5 version.
452
required then we use StringBuilder
When we use String, StringBuffer and StringBuilder
• If the content is fixed and would not change frequently then we use String.
• If content is not fixed and keep on changing but thread safety is required then
we use StringBuffer
• If content is not fixed and keep on changing and thread safety is not

Suppose that we have any string like "Features of Java_Language" when we
use stringTokenizer this string is split into tokens whenever spaces and
STRINGTOKENIZER IN JAVA
StringTokenizer in Java
It is a pre defined class in java.util package can be used to split the given string
into tokens (parts) based on delimiters (any special symbols or spaces).
special symbols present. After split string are :
453

Example
• Features
• of
• Java
• Language
Methods of StringTokenizer
• hasMoreTokens()
• nextToken()
hasMoreTokens()
It is predefined method of StringTokenizer class used to check whether given
StringTokenizer having any elements or not.
nextToken()
Which can be used to get the element from the StringTokenizer.
454

System.out.println("The tokens are: ");
while(st.hasMoreTokens()) {
String one=st.nextToken();
System.out.println(one);
}
}
}
man
455
Output
The tokens are:
He
is
a
ge
ntl
e
Example of StringTokenizer:
import java.util.*;
class Stringtokenizerdemo {
String str="He is a gentle man";
StringTokenizer st=new StringTokenizer(str," ");

Data Conversion
In java programming we have six data conversion technique they are:.
1 Converting numeric string type data into numerical / fundamental
type values
In order to convert numerical string into numerical or fundamental values we
use the following generalized predefined method which is present in wrapper
classes.
Example
String s1="100";
int x=Integer.parseInt(s1);
Example
String s2="100.75f";
Float y=Float.parseFloat(s2);
DATA CONVERSION IN JAVA
456
Here xxx represent any fundamental data type.

Here XXX represent any fundamental data type values
Example
int a=10;
2 Converting numeric / fundamental type values into string type values
In order to convert numeric / fundamental type values into string values, we
use the following predefined static overloaded method.
457

3 Converting fundamental type values into object type values:
In order to convert the fundamental data into equivalent wrapper class object
type data we use the following generalized predefined parameterized
constructor by taking fundamental data type as a parameter.
458

in JDK 1.4 converting fundamental data type values into wrapper class object is
known as boxing. In the case of JDK 1.5 and in higher version it is optional to
the java programmer to convert fundamental data type value into equivalent
wrapper class object. That is implicitly taken care by JVM and it is known as
auto boxing.
Definition of auto boxing
The process of implicitly converting fundamental type value into equivalent
wrapper class object is known as auto boxing.
459

4 Converting object type value into fundamental type value:
In order to convert wrapper class object data into fundamental type data, we
use the following predefined instance method present in each and every
wrapper class.
460

In case of JDK 1.5 and in higher version it is optional to the java
programmer to convert object data into fundamental type data and this
process is known as auto un-boxing and its takes care by JVM. Definition
of auto un-boxing
In process of implicitly conversion objects type data into fundamental type
data is known as auto un-boxing.
461

5 Converting String type data into object type data
In order to convert String type numeric data into equivalent wrapper class
object, we use the following predefined parameterized constructor by each and
every wrapper class except character class.
462

To convert wrapper class object type data into string type data we use the
following generalized predefined instant method which is present each and
every wrapper class.
463
6 Converting wrapper class object type data into String type data

464

Example
int a=10;
• String is=String.valueOf(a);
• Integer io=new Integer(is);
• int x=io.intValue();
• Integer io=new Integer(n);
• String so=io.toString();
• int x=Integer.parseInt(so);
465

BOXING AND UNBOXING IN JAVA
Boxing and Unboxing in Java
Definition of Auto Boxing
The process of implicitly converting fundamental type values into the
equivalent wrapper class object is known as auto boxing.
Converting fundamental type values into object type values:
In order to convert the fundamental data into equivalent wrapper class object
type data we use the following generalized predefined parameterized
constructor by taking fundamental data type as a parameter.
ND DEVELOPMENT
466
SCION RESEARCH A

In JDK 1.4 converting fundamental data type values into wrapper class object is
known as boxing. In the case of JDK 1.5 and in higher version it is optional to
the Java programmer to convert the fundamental data type value into the
equivalent wrapper class object. That is implicitly taken care by JVM and it is
known as auto boxing.
Definition of auto Unboxing.
In process of implicitly conversion objects type data into fundamental type
data is known as auto un-boxing.
Converting object type value into fundamental type value:
In order to convert wrapper class object data into fundamental type data, we
use the following predefined instance method present in each and every
wrapper class.
467

In case of JDK 1.5 and in higher version it is optional to the Java programmer
to convert object data into fundamental type data and this process is known
as auto un-boxing and it takes care by the JVM.
468

JAVA SCANNER CLASS IN JAVA
Java Scanner Class in Java
Scanner is one of the predefined class which is used for reading the data
dynamically from the keyboard.
Import Scanner class
Import Scanner Class in Java
java.util.Scanner
Constructor of Scanner Class
Scanner(InputStream)
This constructor create an object of Scanner class by talking an object of
InputStream class. An object of InputStream class is called in which is created
as a static data member in the System class.
Syntax of Scanner Class in Java
Scanner sc=new Scanner(System.in);
469
Here the object 'in' is use the control of keyboard

470

471

Method Description
1 public byte nextByte() Used for read byte value
2 public short nextShort() Used for read short value
3 public int nextInt() Used for read integer value
4 public long nextLong() Used for read numeric value
5 public float nextLong() Used for read numeric value
6 public double nextDouble() Used for read double value
7 public char nextChar() Used for read character
8 public boolean nextBoolean() Used for read boolean value
9 public String nextLine()
Used for reading any kind of data in the form
of String data.
472
the form of String data.
Method 1 to 8 are used for reading fundamental values from the keyboard.
Method 9 (public String nextLine() ) is used for reading any kind of data in
Instance methods of Scanner Class

For Remember all above methods
From method 1 to 8 combindly we represent as public xxx nextxxx(). Here xxx
represents any fundamental data type. These methods are used for reading the
fundamental data from keyboard.
Accept two values dynamically from the keyboard and compute sum.
Example of Scanner Class in Java
import java.util.Scanner
public class ScannerDemo
{
public static void
main(String args[])
{
Scanner s=new
Scanner(System.in);
System.out.println("Enter
first no= ");
473
int num1=s.nextInt();

System.out.println("Enter second no= ");
int num2=s.nextInt();
System.out.println("Sum of no is= "+
(num1+num2));
}
}
474
Output
Enter first no=4
Enter second no=5
Sum of no is=9

475
System.out.println("Sum= "+res);
}
}
Output
Enter first number: 5
Enter second number: 6
Sum= 11
Program which is accept two number as a string and compute their
sum.
Example
import java.util.Scanner;
class Dataread {
{ Scanner s=new Scanner(System.in);
System.out.println("Enter first number: ");
String s1=s.nextLine();
System.out.println("Enter second number: ");
String s2=s.nextLine();
int res=Integer.parseInt(s1) +
Integer.parseInt(s2);

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