Java

UNIT - I
CHAPTER – 1
java

1

CONTENTS
1. INTRODUCTION
1.1. history of java
2. STRUCTURE OF JAVA PROGRAM
2.1. standard program and Applets
2.2. packages
2.3. importing classes and Packages
3. THE JAVA COMPILER AND VIRUTAL MACHINE
4. DOCUMENTATION COMMENTS
5. DATA TYPES

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6. METHODS
6.1. parameters
6.2. Overloaded Methods
7. EXCEPTIONS
7.1. throwing an exception
7.2. handling exceptions
8. ACCESS MODIFIERS
9. INHERITANCE AND METHOD OVERRIDING
9.1. Super-classes and Subclasses
10. GENERIC METHODS
11. GARBAGE COLLECTION
12. RECURSION
12.1. recursive function
12.2. induction
12.3. recursive methods
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13. TESTING AND DUBUGGING
13.1. what is testing
13.2. designing test data
13.3. debugging

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1. INTRODUCTION
1.1. HISTORY OF JAVA

1. Java programming language is usually associated
with “ World Wide Web ”.
2. Java predates the Web.
3. Java began it’s life as the programming language
“ Oak ”.
4. Oak was developed by the “Green Project Members”
* Patrick Naughton
* Mike Sheridan
* James Gosling
5. A group formed in 1991 to create products for the
“ Smart electronic Markets “
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6. The existing programming language were not
suitable for “ consumer electronics “.
7. The Chief Programmer of Sun Microsystem –
James Gosling :
created the software for controlling
“ Consumer Electronic devices “.
8. The team wanted a fundamentally new way of
computing , based on the power of “ Networks “.
And the S/W to run on different kinds of computers

9. Patenting issues gave a new name to Oak – Java.

10. HotJava
- The first Java-enabled Web browser
6

ChaRaCTERISTICS Of java
• Java is simple
• Java is object-oriented
• Java is distributed
• Java is interpreted
• Java is robust
• Java is secure
• Java is architecture-neutral
• Java is portable
• Java is high-performance
• Java is multithreaded
• Java is dynamic language
7

• Java is simple
Java is simple language, can be learned easily.
• Java is object-oriented
Java provides Abstraction, Encapsulation,
Inheritance and Polymorphism.
• Java is distributed
Java is tuned to the Web, So java program can
access data – across the Web as easily as they access
data from local system.
• Java is interpreted
Java is both Interpreted and compiled. The code
is complied to byte code that’s “ Binary “ and “
platform independent”.
8

• Java is robust
Java forces the programmer to handle
unexpected errors. This ensure that java programs are
“Robust” (Reliable) and bug free and don’t crash.
• Java is secure

A program traveling from internet to pc could
possibly carry a virus. Java done strong type-checking
on the user-machine, and changes in the program are
tagged as errors and program will not executed. So,
java is “secure”.
. Java is architecture-neutral
The byte code can be executed on a variety of
computers running on different operating systems.
9

• Java is portable

Java program can run on any machine that has
a java interpreter. Other people can use the programs
written in java, even if they have different machines
with different operating systems.
• Java is multithreaded

perform multiple task at the same time.
• Java is dynamic language

Maintaining different versions of an
application is very easy in Java.

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2. STRUCTURE Of java
• PROGRaM
Types of Java Programs are:
1. Applications (or) stand-alone program
- they are program that don’t need a browser
to run simultaneously.
- need MS-DOS or UNIX prompt to execute
the program.
2. Applets
- Applets are programs that execute inside
a Web page.
- Applets require a Java enabled browser like
* MS-internet Explorer
* Netscape Navigator
* Hotjava 11
- Applet have Graphical User Interface.

3. Servlets
- these programs extend the functionality of
web servers
4. Packages
- they are collections of classes that can be
shared by other Java programs.

12

2.1. standard program and Applets
• Every java program is a – CLASS
• Every class may contain data and METHOD members

S. No Application applet
1. METHOD name is “ main” METHOD name is “ int”

2. Syntax for Compiling Syntax for Compiling
javac <filename.java> javac <filename.java>

3. Syntax for Executing Syntax for Executing
java filename Appletviewer <URL.html file>

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2.2. packages
• DEFINITION
A Package is a collection of classes that can be
shared by java program.
Packages are used to organize classes into
groups.
• Types of Packages

(i). Pre-defined (ii). User-defined
1. java.lang
2. java.util user can
3. java.applet create their
4. java.awt own packages
5. java.io ( Refer Slide Nos from

6. java.net 106 to 122)
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1. java.lang
- provides classes and interfaces that are
fundamental to java programming.
2. java.util
- provides classes that support collections, data and
calendar operations, parsing, internationalization

and basic event processing. Also refers to all
programs in the directory (lang/java or
langjava).
3. java.applet
- provides classes, necessary for basic applet
programming.
4. java.awt (abstract window toolkit) 15
- provides classes for creating GUI programs.

5. java.io
- provides classes for reading and writing data in
the form of streams. (input stream, output stream)
e.g: memory, file, buffer, network
6. java.net
- provides classes that provide network
programming.

16

2.3. importing classes and Packages
Syntax for package
• import <package_name>.*;
• import <package_name> . <class_name>;

Example:
import java.awt.*;
import java.awt.Button;

import java.awt.*;
in this syntax all the classes in awt package have to

imported
import java.awt.Button;
in this syntax only button class from awt package
have to imported 17

3. ThE java COMPIlER aND vIRTUal
MaChINE
• Java source code is converted into Java Byte code
(or) J-code.
* When the program <programName> is compiled, the
program source code is read from the file
<programName.java>
* The compiled byte code is written in the file
<programName.class>
* Java Virtual Machine (JVM) is a software that
interpret and executes the byte code.
• The main task of JVM is – the loading of .class files
• JVM- has class loaders that loads the .class files, and
executed by the execution engine.

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• Each java applications run inside a JVM.
• JVM starts when you start a java program and
terminates when the program ends.
• The no. of JVM starts when you start a java program
and terminates when the program ends.

• CLASS LOADER ARCHITECTURE
1. A JVM can have many class Loader. They provide

security and network to java programs.
2. The JVM has two types of class loaders.
(a) Primordial Class Loader
(b) Class Loader Objects
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(a) Primordial Class Loader
A primordial Class Loader is a part of the JVM
implementation. It loads the java API classes when
you execute a java program.
(b) Class Loader Objects
An application can create many class loaders at
runtime for loading the classes of the application.

Implementation of Class Loader

Class Loader Class Loader

Java Virtual Machine Implementation
Primordial Class Loader Java API

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JAVA VIRUTAL MACHINE

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• Through the Java VM, the same application is capable
of running on multiple platforms.

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• The Java platform has two components:
– The Java Virtual Machine (JVM)
– The Java Application Programming Interface (API)

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4. DOCUMENTaTION COMMENTS
• A comment is a message for a programmer &
describes a class, a method, or even a statement.
The complier ignore what you write as comments
• Comments are ignored by the compiler but are
useful to other programmers
• Java support three styles of comments:
1. Multiple line comments
2. Single line comment entries
3. The javadoc comments
1.Multiple line comments
Anything you write between /* and */ is treated
as a comment. The text that you type here can cover
many lines.
/* multiple line comments */ 24

2. Single line comment entries
anything you type after // is treated as a comment.
The text can’t span (extend) more than a line. If you
have multiple lines as comments, you must start
every line with //.
// single line comment
3. The javadoc comments
these lines are used by the javadoc utility to create
documentation. These comments are similar o the
multiple line comments but start with a /** instead
of /*
/** this is a javadoc comment*/

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5. DaTa TYPES
• The data that’s stored in memory can be of many
types. For example:
* a person’s age is stored as a numeric value & an
address is stored as alphanumeric characteristics.
* an address is stored as alphanumeric characters
Data types are used to define the operations possible on
them and the storage method.

* The data types in java are classified as:
1. primitive (or) standard data types
2. Abstract (or) derived data types

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1. primitive (or) standard data types

Data Type Size/Format Description Range
(Numbers)

Byte 8-bit Byte-length -128 to +128
integer If signed(-2 7 to
27 -1)
If unsigned(0 to
255)

Short 16-bit Short integer -32768 to
+32767(-215 to
215-1)
Int 32-bit Integer -231 to 231-1

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Data Type Size/Format Description Range
(Numbers)

long 64-bit Long integer -2 63 to 2 63-1

float 32-bit Single- +/-about 10 39
precision
floating point

double 64-bit Double- +/-about 10 317
precision
floating point

(other types)
Char 16-bit A single character

Boolean 1-bit A Boolean value (true or false)
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2. Abstract (or) derived data types

• Abstract data types are based on primitive data types
and have more functionality than primitive data
types.
• Example
“String” is an abstract data type that can store
letters, digits and other characters like /,(), : , ; , $ , #

* “String ”provides methods for concatenating two
strings, searching for one string within another, and
extracting a portion of a string. The primitive data
types don’t have these features.

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6. METhODS
1. parameters
• A method is a body of code that’s used for performing
a set of tasks. The behavior of an object is determined
by the program.
• Declaring Methods:

syntax:
[<access_specifier>] [<modifiers>] <return_type>
<method_name> ([argument_list])
{
//statements
}
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• Example:
public static int abc (int a, int b, int c)
{
return a+b*c+b/c;
}
Where:
abc - name of the method
int - return type of the method is ‘int’
(int a, int b, int c) – formal paramenters of the
method abc, each is of integer
type.

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• If the method is invoked by the statement
Z = abc (2,x,y)
then 2,x,y are the ‘actual parameter’.

* when the method ‘abc’ is invoked the
a - is assigned to 2
b - is assigned to x
c - is assigned to y
* In java all method parameters are ‘value parameters’.
* At run time the value of each ‘actual parameter’ is
copied into the corresponding format parameter before
the method is executed.
32

2. Overloaded methods
• Overloading is a technique in which more than one
method having the same name can be present in a
program. The compiler resolves the method to be
invoked using the signature of the method.
• Function signature
1. The name of the method
2. The number of arguments it takes
3. The data type of the arguments
4. The order of the arguments
- when we call a method, the compiler uses the signature
of the method to resolve the method to be invoked.
- A class can’t have two methods having the same
signature.
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- this is because the compiler will not know which
method to invoke if more than one method has the same
signature.
Example:
java supports method overloading and hence, the
methods can be declared as follows:
* public void add(int a, int b); // add two integers
* public void add(float a, float b); // add two floats
* public void add(float a, int b); // adds a float and
an integer
* In the following example the ‘calculator’ class, the
methods have the same name but different
parameters and the signatures of the methods are
different. 34

class calculator
{
public int add(int a, int b)
{
System.out.println("int and int");
return a + b;
}

public float add(float a, float b)
{
System.out.println("float and float");
return a + b;
}
35

public float add(float a, int b)
{
System.out.println("float and int");
return a + b;
}
public static void main(String args[])
{
calculator c = new calculator();
System.out.println(c.add(1,10))
System.out.println(c.add(1.6f,10.5f));
}
} 36

class calculator
{
public int add(int a, int b)
{
System.out.println("int and int");
return a + b;
}

public float add(float a, float b)
{
System.out.println("float and float");
return a + b;
}
38

public float add(float a, int b)
{
System.out.println("float and int");
return a + b;
}
{
calculator c = new calculator();
System.out.println(c.add(1,10))
System.out.println(c.add(1.6f,10.5f));
System.out.println(c.add(10.5f,2));
}
}
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7. EXCEPTIONS
• An exception is defined as an ‘abnormal’ event that
occurs during program execution and disturb the
normal flow of instructions.
• Error-handling becomes necessary, when developing
applications and need to take care of unexpected
situations.
• The unexpected situations that may occur during
program execution are:
* Running out of memory
* Resource allocation errors
* Inability to find files
* Problems in network connectivity

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Exception-Handling Techniques
• When an unexpected error occurs in a method, java
creates an object of the types ‘ Exception’.
• After creating the Exception object, java sends it to
the program, by an action called “throwing an
exception”.
• The Exception object contains information about the

- type of error
- status of the program when the exception occurred
* Key words in Excepting:
try
catch
throw
throws 42

• Try Block
syntax:
try
{
//statements that may cause an exception
}
* If an exception occurs within the try block, the
appropriate exception-handler that’s associated
with the try block handles the exception.
* A try block must have at least one catch block
that follows it immediately.

43

• catch Block
syntax:
try
{
//statements that may cause an exception
}
catch(……)
{
// error handling routines
}
• The catch statement take the object of the exception
class that refers to the exception caught.
• Once the exception is caught, the statements within
the catch block are executed.
• The scope of the catch block is based on the statement
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in the preceding try block.

Exception handling mechanism
• In java, exception-handling facility handles abnormal
& unexpected situation in a structured manner.
• When an exception occurs, the java runtime system
searches for an exception-handler (try-catch-block).
• If a handler is not found in the current method, the
handler is searched for in the ‘calling method’.
• The searches goes on till the runtime system finds an
appropriate exception-handler.
• EXAMPLE:
// derivedclass.java
class baseclass
{
public int divide(int num1, int num2)
{ 45

return num1 / num2;
}
}
public class derivedclass extends baseclass
{
public int divide(int a, int b)
{
return super.divide(a,b);
}
{
int result = 0;
derivedclass d1 = new derivedclass();
46

try
{
result = d1.divide(100, 0);
}
catch(ArithmeticException e)
{
System.out.println(“Error…division by zero”);
}
System.out.println(“The result is: “ + result”);
}
}

47

Multiple catch block - example

public class trycatch
{
{
int num1, num2, result = 0;
num1 = 100;
num2 = 0;
try
{
result = num1/num2;

}

49

{
System.out.println("Error---division by zero");
}
catch(ArrayIndexOutOfBoundsException e)
{
System.out.println("Error----out of bounds");
}
catch(Exception e)
{
System.out.println("some other error");
}
System.out.println("The result is: " + result);
}

}
50

EXAMPLE-2

public class trycatch
{
{
int num1, num2, result = 0;
num1 = 100;
num2 = 4;
try
{
result = num1/num2;

}
52

{
System.out.println("Error---division by zero");
}
catch(ArrayIndexOutOfBoundsException e)
{
System.out.println("Error----out of bounds");
}
catch(Exception e)
{
System.out.println("some other error");
}
System.out.println("The result is: " + result);
}

}
53

throw statement
• When a user enters a wrong login-ID (or) password,
the throw statement is used to throw an exception.
• The throw statement takes a single statement, which
is an object of the ‘Exception class’.
• Syntax
throw Throwableinstance;
* Example
throw ThrowObject;
• The compiler gives an error if the object ‘ThrowObject”
doesn’t belong to a valid ‘Exception class’.
• The ‘throw statement is commonly used in
‘programmer-defined’ exceptions.
55

throws statement
• Throws statement is used to specify that ‘ an exception
has to be handled by the calling method. It’s used for an
exception that a method is capable of raising, but not
handling.
• Syntax
[<access_specifier>][<modifier>]<return_type>
<method_name> (<arg_list>) [throws <exception_list>]
• Example
public void acceptpassword() throws IllegalAccessException
{
System.out.println(“ intruder !!”);
throw new IllegalAccessException;
}

56

Finally Block
• The finally block is used when it’s necessary to
process certain statements no matter, whether an
exception is raised or not.
• Example
try
{
openFile();
writeFile(); // may cause an exception
}
catch(……..)
{
// process the exception
}
Finally
{ closeFile();
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}

Common exceptions

1. ArithmeticException Exception

2. NullPointerException Exception

3. ArrayIndexOutofBoundsException Exception

58

8. ACCESS MODIFIERS
• An access specifier determines which features of a
class (the class itself, the data members, and the
method) may be used by the other classes.
• Java supports three specifiers (or) Access Modifiers
1. public
2. private
3. Protected
4. Default
1. Public access specifier
A class, data member (or) method that has a public
access specifier can be accessed by any object. An
inner class can’t have a public access specifier.
59

• Syntax
<access_specifier> <return_type> <method>
([argment list])
{ ----------
}
Example:
public class employee
{
string empname;
string empadd;
public void displaydetails( )
{
// place the code for displaying employee
details
}
} 60

2. Private access specifier
• Only object of the same class can access a variable or
a method that has a private access specifier. The
variables and method of the inner classes can be
declared as private.
• Example:
private int privateVariable;

3. Protected access specifier
variable, methods, and inner classes that are declared
protected accessible to the subclasses of the class in
which they are declared.
Example:
protected int protectedVariable
61

4.Default access
A class, a variable or a method that doesn’t have an
access specifier as private, public, protected is said to
have default access. These classes, variables or
methods are accessible to all the classes of a package.
Example:
consider following set of classes y and z inherit from
class x. class z belongs to the package p1 and classes
x and y belong to the package p2.

Package p1

Class X Package p2

Class Z
Class Y
62

* A method accesme() has been declared in class X. The
following table shows the accessibility of the method
accessme() from class Y and Z.

Access specifier Class X Class Y
accessme() is Accessible as Y is Accessible as z is
declared as a subclass a subclass (even
protected if it’s in another
class)
accessme() is Accessible as it is Not accessible as
declared without in the same it is not in the
an access package same pckage
speicifer

63

Access Specifier Member Visibility
Default Member is visible only to
classes in the same
package.
Private Member is visible only
within the class C.
Protected Member is visible to all
classes in the same
package and to
subclasses of c in other
packages.
Public Member is visible to all
classes in all packages.
64

MODIFIERS
• Modifiers determine how the data members and
methods are used in other classes and objects.
• The modifiers in java:
1. static
2. final
3. abstract
4. native
5. transient
6. synchronized
7. volatile

65

9. INHERITANCE AND METHOD
OVERRIDING
• Inheritance is a situation in which a class derives a
set of attributes and related behavior from a parent
class.
• 9.1. super classes and subclasses:
* super class:
super class is a class from which another class
inherits properties. It share its properties with its
child classes.
* sub class:
sub class is a class that inherits attributes and
methods from a super class.
66

• Super class some times referred to as the ‘base class’
and the subclass is referred to as the ‘derived class’.
• Subclass don’t inherit the constructs of the super
class.
• Example:
let us take the example of ‘air tickets’- it can be of two
types. Confirmed and request ticket. both the
tickets have a lot of common attributes. For
example
flight_number, date, time and destination.
confirmed ticket would have a ‘seat number’, while
a request ticket would have a ‘status’.

67

• Example:
Ticket

RequestTicket ConfirmedTicket

Syntax:

public class <subclass name> extends <superclass
name>

public class confirmedTicket extends Ticket

68

Final keyword
• The final modifier doesn’t allow a class to be
inherited. A method declared anal can’t be overridden
by a subclass.
• Final- keyword can prevent people from extending a
class by using the ‘final’ modifier as follow:
example:
final class password
{
--------
}

69

OVERRIDING METHODS
• In overridding, a subcalss method overrrides the
definition of a super class method, if the method
defined in the subcalss has the same signature of a
method in the super class.
• Example:
let us consider the class ‘wheelchair’ is derived
from the ‘chair class’. Both the classes have a
method called ‘adjustHeight()’. Wheelchair is
adjusted differently form the way other chairs are
adjusted. Therefore, the wheelchair class overrides
superclass method ‘adjustHeight()’.

70

// declaring base class chair (saved as wheelchair.java)
class chair
{
public void adjustHeight()
{
System.out.println(“adjusting chair height”);
}
}
//deriving wheelchair class from chair
public class wheelchair extends chair
{
public static void main (String args[])
{ wheelchair w
w = new wheelchair();
w.adjustHeight();
}
} 71

// declaring base class chair (saved as wheelchair.java)
class chair
{
{
System.out.println(“adjusting chair height”);
}
}
//deriving wheelchair class from chair
public class wheelchair extends chair
{
//overriding adjustHeight() method
{ System.out.println(“adjust wheelchair height”);
} 73

public static void main (String args[])
{ wheelchair w
w = new wheelchair();
w.adjustHeight();
}
}

74

10. GENERIC METHODS
* The following two programs differ only in the data
types of the formal parameters & the return value.

Program-1:
Public static int abs(int a, int b, int c)
{
return a+b*c+b/c;
}
Program-2:
Public static float abc(float a, float b, float c)
{
return a+b*c+b/c;
}
76

• Write a new version of the code for every data type of
the formal parameters & return value – we can write
a ‘generic code that’s independent of this data type.
• It’s not possible to write generic methods to work
with actual parameters of any of java primitive data
types.
• Generic methods can be written to work with actual
parameters of the type object (or) any subclass of
object.
• Example:
generic methods will work with the wrapper classes
of java, because these wrapper classes are
subclasses of ‘object’.

77

wrapper classes
• A wrapper class extends the functionality of the
primitive data types. It allows an object to be created
from a primitive data type.
• Variables that are declared using ‘primitive data types’
aren’t objects.
• To make primitive types to behave like objects, theses
wrapper classes also provide methods for converting
strings to various data types.
• Example:
represent a set of primitive data types like ‘int’, it can
be done in at least two way:
1) create an array of actual size:
int x[] = {10,20,30};
78

2) the other way is to use a wrapper class:
Integer x[] = {new integer(10), new Integer(20),
new Integer(30)};
• In terms of speed & memory space, the first statement
is more efficient for representing a set of values.
• The wrapper classes in java.lang are:
s.no. Primitive data types Wrapper classes
1. byte Byte
2. char Char
3. int Int
4. long Long
5. float Float
6 double Double
7. boolean Boolean
8. short Short 79

INTERFACE
• An interface contains constant values and method
declarations. The difference between a class and
interface is that the methods in an interface are only
declared and not implemented.
• Interfaces are used to define a ‘behavior protocol’
(standard behavior) that can be implemented by any
class anywhere the class hierarch.
• Syntax:
An interface is declared like a class, but the keyword
‘class’ is replace by the keyword ‘interface’. The
declaration of an ‘interface’ is shown below:
public interface interfaceName // interface declaration
{
// interface body

} 80

• Example:
public interface color
{
final int white = 0;
final int black = 1;
final int red = 2;
}
• Example:
consider the devices TV & VDU, both of them require
a common functionality as far as brightness control is
concerned. This functionality can be provided by
implementing an interface called “Brightnesscontrol”
which is applicable for both the devices.
81

// interface definition of Brightnesscontrol
public interface BrightnessControl
{
void increaseBrightness();
void decreaseBrightness();
}
// TV class implementing the interface
public class TV implements Brightnesscontrol
{
void increaseBrightness()
{
// implementation code
}
82

void decreaseBrightness()
{
}
}

//VDU class implementing the interface
public class VDU implements BrightnessControl
{
void increaseBrightness()
{
}
83

Void increaseBrightness()
{
}
}

84

Steps for implementing an Interface

1. Import the interface
2. Declare the class and use the implement keywords
followed by the name of the interface.
3. Ensure that the class implements every method that

has been declared in the interface.
4. Save the file with the .java extension.
5. Compile the applet or application created.

85

Example program
// implementinterface.java
// example of an interface
Import java.lang.*;
{
public String displayText(); // no implementation of method

}

public class implementinterface implements inter
{
implementinterface inter = new implementinterface();
String str = inter.displayText();
System.out.println(str);
} 86

public String displayText()
{
return “ Good Morning”;
}
}

Out put:

Good Morning

87

11. GARBAGE COLLECTION
• When a program stops referencing an object the object
is not required any more and becomes garbage.
Garbage collection is a process that automatically
frees the memory of objects that are no more in use.
• Garbage collector must do two things:
1. Detect garbage objects
2. De-allocate the memory of garbage objects and
make it available to the program.
• There are different garbage collection algorithms (or)
there are different approaches used for detecting
garbage objects are as follows:

* Reference-counting garbage collectors – keep a
count of the references for each live object.
88

*Tracing collectors (or) mar-and-sweep algorithm
- the mark phase marks all the referenced objects.
The sweep phase collects the memory of
unreferenced objects.
* Compacting collectors
- reduce fragmentation of memory by moving all the
free space to one side during action.

* Adaptive algorithm
- monitors the situation and uses the garbage
techniques that best suits the situation.

The finalize( ) method
- before freeing the memory associated with an object,
the garbage runs the ‘finalize() method’. 89

• Finalize method is declared in any class. The finalize()
method is declared as follows:

protected void finalize() throws Throwbale
{
super. finalize( );
}
* Garbage collector is called manually using the
‘system.gc ( ) method.’

90

12. RECURSION
• Recursive method invokes itself. There are two types
of recursions
(i) Direct recursion
- the code for method ‘ f ‘ contains a statement that
invokes ‘ f ’.
(ii) Indirect recursion
- method ‘ f ‘ invokes a method ‘ g’ , which invokes a
method ‘h’. and so on, until method ‘ f ‘ is again
invoked.
12.1.Recursive Functions
The factorial function is defined as follow:
f(n) = 1 n<=1
nf(n-1) n>1

This definition states that f(n) = 1 whenever n is less than or
equal to 1.
91

• When ‘ n ‘ is less than 1, f(n) is defined recursively
• Example
f (n) = nf(n-1); f(3) = 3*f(3-1) = 3*f(2) = 3*2 = 6
• For a recursive definition of f(n), the f must meet the following
requirements:

* The definition must include a base component in which f(n)
is
defined directly, (i.e. non-recursively) for one or more values
of n.
e.g. from the above equation the base is
f(n) = 1 for n<=1

* In the recursive component all occurrence of ‘f’ on the right
side should have a parameter smaller than ‘n’, so that
repeated application of the recursive component transforms
all occurrences of ‘f’ on the right side.
92

• repeated application of the recursive components transforms
f(n-1) to f(n-2), f(n-3)……. and finally f(1).
(e.g)
repeated application of the recursive component gives the
following:

f(5)=5f(4)=20f(3)=60f(2)=120f(1)=120
i.e. f(5)=120

12.2.Induction
• In a proof by induction, the validity of claim is established as
follow: n

∑ i=n(n+1)/2, n>=0
i=0

• This method has three components to make a proof
1. induction base
2. induction hypothesis
93
3.induction step

• 12.3.Recursive Methods

a proper recursive method must include a base component.

Public static int factorial(int n)
{
if ( n < = 1)
return 1;
else
return n * factorial (n-1);
}

94

13. TESTING AND DUBUGGING
13.1. what is testing
Correctness is the most important attributes of a
program.
* program Testing:
providing mathematical proof of correctness for a
small program is difficult.
• Test data:
- compare the program behavior with the expected
behavior.
- if these two behaviors are different program
having problem.

95

- if these two behaviors are same also, we couldn’t
conclude that the program is correct, if the
behavior isn’t same on other input data.

• Test data: (Definition)
Execute the program on the target computer using
input data is called “Test Data”.

• Test Set:
The subset of the input data space that’s actually
used for testing is called the “Test set”.

Example: (Quadratic Roots)
A Quadratic function (or) quadratic in x is a function

that has a form
ax2 + bx + c 96

where
a, b, c - real numbers and a = 0

examples for quadratic not a quadratic
functions functions
3x2-2x+4
-9x2-7x 5x+3
3.5x2+4
5.8x2+3.2x+5

The roots of a quadratic function are the values of ‘x’
at which the function value is 0.

97

• Example:

(1) f(x) = x2-5x+6
if x = 2
f(2) = 22 -(5*2)+6
= 4 -(5*2)+6
= 4-10+6
= -6+6
= 0

(2) f(x) = x2-5x+6
if x = 3
f(2) = 32 -(5*2)+6
= 9 -(5*3)+6
= 9-15+6
= -6+6
= 0

98

• Every quadratic has exactly two roots, and these roots
are given by the following formula:
-b + b2 – 4ac
____________________
2a
if the function
f(x) = x2-5x+6 and a=1, b=-5, c=6 then

= -(-5) + -52 – 4*1*6
___________________
2*1
=5+1 5–1
2 ; 2
f(x) = (3,2) 99

Designing Test data
• Objectives of Testing
expose the presence of error
• Correctness of the programs depends on – if the
designed data fails to expose errors.
• Example:
Quadratic Roots
- behavior of any test data may be verified in one of
two ways:
first:
find out the roots of the test quadratic
(e.g) before slide
(a, b, c) = (1, -5, 6)
100

second:
- substitute the roots(answers(3,2)) produced by
the program into the quadratic function.

-and verify the function value is 0

Example:

f(x) = x2-5x+6

(i) If f(3) = 32-5*3+6 (ii) if f(2) = 22-5*2+6
= 9 – 5*3+6 = 4-5*2+6
= 9-15+6 = 4-10+6
= -6 + 6 = -6+6
= 0 = 0
101

Data Testing Techniques
• There are two categories in data testing techniques
(i) Black Box Method
(ii) White Box Method
(i) Black Box Method
while developing test data, consider only program’s

function, not the actual code.
* the most popular black box methods are
I/O partitioning
cause-effect graphing
* In I/O partitioning the input and output data
are partition into classes.
* Data in different classes cause the program
to exhibit qualitatively different behaviors.
* Data in same class cause qualitatively similar102
behaviors.

• Example:
The quadratic roots has three different qualitatively
behaviors:
1. the roots are complex
2. the roots are real and distinct
3. the roots are real and the same.
Each behaviors has different kinds of behaviors.

(ii) White Box Method
while developing test data, consider only program’s
actual code.
* Statement coverage:
the weakest condition we can place on a test set, will
execute the program statement at least once.
103

• Decision coverage
the test set cause each condition in the program to
take on both true and false values.
• Clause coverage
strengthen the decision coverage criterion to require
each clause of each condition to take on both true and
false values. The strengthen criterion is called “ clause
coverage”.
clause
it is defined as Boolean expression that contains no
Boolean operator (i.e., &&, ||, ! ).
(e.g) x > y, x + y < y * z

104

Debugging
• The process of determining and correcting the
difference between the desired and observed behaviors
is called “ debugging”.
• Suggestions for debugging:
1. Try to determine an error by logical reasoning.
2. Errors should be corrected first by determining
their cause and then redesigning your solutions as

necessary.
3. After corrected an error, the correction doesn’t
result an errors.
4. When testing and debugging a multi-method
program, begin with a single method that’s
independent.This method is typically i/p & o/p
method. Then introduce additional methods one at
at a time. This is called as “ incremental testing &
105

USER DEFINED PACKAGE
PROGRAM

106

Design and develop a Package in Java which contains
following Sorting techniques
a) Bubble Sort
b) Selection Sort

c) Shell Sort

107

Steps in creating “ User Defined Program”
Step -1 : Create a folder name of your User defined package in the path, where

the java is installed
Example:
►Create a Folder Name “BUBBLE”
► Click the Folder (BUBBLE) and save your java file name
(bubblesort.java)
► Click the Folder (SELECTION) and save your java file name
(selectionsort.java)
►Create a Folder Name “SHELLSORT”
► Click the Folder (SHELLSORT) and save your java file name
(shellsort.java)
Step-2: Creation of Main Program
Example:
►save the main program (sort.java) in the bin path
(e.g: C:Program FilesJavajdk1.5.0bin>
108

// package for bubble sort
package BUBBLE;
import java.io.*;
public class bubblesort
{
int a[]=new int[10];
int n,t;
InputStreamReader isr=new InputStreamReader(System.in);
BufferedReader br=new BufferedReader(isr);
public void bdisplay()
{ try
{
System.out.println("n--->BUBBLE SORT<----n");
System.out.println("Enter N values to sort..");
n=Integer.parseInt(br.readLine());
System.out.println("Enter" + n + "Value one by one..");
for(int i=1; i<=n; i++)
109

{
a[i] = Integer.parseInt(br.readLine());

}
System.out.println("n Before Sortingn");

{
System.out.println(a[i]+ " ");
}
{

for(int j=1; j<=n; j++)

{
if(a[j]>a[j+1])
a[j]=(a[j]+a[j+1])-(a[j+1]=a[j]);
}
}

110

System.out.println("n After Sortingn");
for(int i=2; i<=n+1; i++)
{
System.out.println(a[i] + " ");

}
}
catch(Exception e)
{
System.out.println("Cause Error..");
}
}
}

111

// package for Selection sort
package SELECTION;
import java.io.*;
public class selectionsort
{
int n,t;
public void sdisplay()
{ try
{
System.out.println("n--->SELECTION SORT<----n");
112

{ a[i] = Integer.parseInt(br.readLine());
}
{
}
{
int min,loc;
min=a[i];
loc=i;
for(int j=i+1; j<=n+1; j++)
{ if(min>a[j])
{
min=a[j];
loc=j;
} 113

a[i]=(a[i]+a[loc])-(a[loc]=a[i]);
}
}
for(int i=2; i<=n+1; i++)
{
}
}
catch(Exception e)
{
}
}
}

114

// package for shell sort
package SHELLSORT;
import java.io.*;
public class shellsort
{
int n,t,incr,j;
public void shdisplay()
{
try
{
System.out.println("n--->SHELL SORT<----n");

115

{
}
incr=n/2;
while(incr>0)
{
for(int i=1;i<n+1;i++)
{
j=i;
t=a[i];
while((j>incr) && (a[j-incr]>t))
{
a[j]=a[j-incr];
j=j-incr;
}
a[j]=t;
} 116

if(incr/3!=0)
incr=incr/3;
else if(incr==1)
incr=0;
else
incr=1;
}
{
}
}
catch(Exception e)
{
}}}

117

//Main Program
import BUBBLE.*;
import SELECTION.*;
import SHELLSORT.*;

class sort
{
public static void main(String[] args)
{
bubblesort bs = new bubblesort();
bs.bdisplay();
selectionsort ss = new selectionsort();
ss.sdisplay();
shellsort sh = new shellsort();
sh.shdisplay();
}
}
118

THANKS FOR WATHING MY -
PPT

PRESENTED BY
KAVITHA.C.R

ASST. PROFESSOR
SLNCS

123

Java

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