What is Java? Presentation On Introduction To Core Java By PSK Technologies

INTRODUCTION TO
CORE JAVA
PSKTECHNOLOGIES
▪ An ISO 9001:2015 (QMS) Certified IT Company
Computer Education | Software Development
|Computer Sales & Services
▪ Plot No-780, Near DurgaTemple, Katol Road Chaoni,
Nagpur-13
▪ Phone: 9975288300 / 9970141466
▪ Email: info@psktechnologies.co.in
▪ website: www.pskitservices.com

Website: www.pskitservices.com
Phone: 9975288300 / 9970141466
 History
 Several Java Version
 Feature of java
 Internal Detail
 JVM
 What is JVM
 Variables
 Data Type in java
 Advantages of naming Convention in java
 CONTENT

 HISTORY
Java is a general, all-purpose computer programming language that is circumstantial, class-
based, object-oriented, and specially designed to have few application dependencies as possible.
Java was developed initially for interactive television, but it was too advanced technology for the
digital cable television industry at the time. It is proposed to let application developers “write once, run
anywhere, suggesting that compiled Java code can run on all platforms that condone Java without
the necessity to recompile. Java applications are compiled to byte code that can run on any Java
virtual machine (JVM) regardless of computer architecture.
James Gosling is generally credited as inventor of the Java programming language
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First version released in 1995,Several java versions have been released, and they are:
 JDK Alpha and Beta (1995)
 JDK 1.0 (23rd Jan 1996)
 JDK 1.1 (19th Feb 1997)
 J2SE 1.2 (8th Dec 1998)
 J2SE 1.3 (8th May 2000)
 J2SE 1.4 (6th Feb 2002)
 J2SE 5.0 (30th Sep 2004)
 Java SE 6 (11th Dec 2006)
 Java SE 7 (28th July 2011)
 Java SE 8 (18th March 2014)
 Java SE 9 (21st Sep 2017)
 Java SE 10 (20th March 2018)

FEATURES OF JAVA
The following are some important features of Java Programming Language:
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 Simple
 Platform Independent
 Architectural Neutral
 Dynamic and Extensible
 Portable
 Multi-Threading
 Distributed
 Networked
 Secured
 High Performance

 Internal Details of Hello Java Program
 What happens at compile time?
At compile time, java file is compiled by Java Compiler (It does not interact with OS) and converts the java code
into byte code.
Java Virtual Machine(JVM)
 What happens At runtime ?
At runtime, following steps are performed:
• Class Loader : Is the subsystem of JVM that is used to load class files
• Byte CodeVerifier: Checks the code fragments for illegal code that can violate access right to objects.
• Interpreter: Read byte code stream then execute the instructions. Website: www.pskitservices.com
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 IMPORTANT DEFINATION
 Class : Keyword is used to declare a class in java.
 Public: Keyword is an access modifier which represents visibility, it means it is visible to all.
 Static : Is a keyword, if we declare any method as static, it is known as static method. The
core advantage of static method is that there is no need to create object to invoke
the static method. The main method is executed by the JVM, so it doesn't require to
create object to invoke the main method. So it saves memory.
 Void : Is the return type of the method, it means it doesn't return any value.
 Main : Represents startup of the program.
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 Valid java main method signature
1. public static void main(String[] args)
2. public static void main(String []args)
3. public static void main(String args[])
4. public static void main(String... args)
5. static public void main(String[] args)
6. public static final void main(String[] args)
7. final public static void main(String[] args)
8. Final strictfp public static void main(String[] args)
 Invalid java main method signature
1. public void main(String[] args)
2. static void main(String[] args)
3. public void static main(String[] args)
4. abstract public static void main(String[] args)

 What is JDK, JRE and JVM
Understanding the difference between JDK, JRE and JVM is important in Java. We are having
brief overview of JVM here.
 JVM
JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime
environment in which java byte code can be executed. JVM (Java Virtual Machine) is an abstract
machine. It is a specification that provides runtime environment in which java byte code can be
executed.
The JVM performs following main tasks:
 Loads code
 Verifies code
 Executes code
 Provides runtime environment
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 JRE
JRE is an acronym for Java Runtime Environment. It is used
to provide runtime environment. It is the implementation of
JVM. It physically exists. It contains set of libraries+ other
files that JVM uses at runtime. Implementation of JVMs are
also actively released by other companies Sun Micro
Systems.
 JDK
JDK is an acronym for Java Development Kit. It
physically exists. It contains JRE+ development tools.

 JVM (JavaVirtual Machine)
JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime
environment in which java byte code can be executed. JVMs are available for many hardware
and software platforms (i.e. JVM is platform dependent).
 What is JVM
It is A specification where working of Java Virtual Machine is specified. But implementation
provider is independent to choose the algorithm. Its implementation has been provided by
Sun and other companies.
An implementation its implementation is known as JRE (Java Runtime Environment).
Runtime Instance Whenever you write java command on the command prompt to run the
java class, and instance of JVM is created.
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 What JVM does?
The JVM performs following operation:
• Loads code
• Verifies code
• Executes code
• Provides runtime environment
JVM provides definitions for the:
• Memory area
• Class file format
• Register set
• Garbage-collected heap
• Fatal error reporting etc.
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 Internal Architecture of JVM
Let's understand the internal architecture of JVM. It contains class loader, memory area, execution
engine etc. it Contain
1. Class loader:
Class loader is a subsystem of JVM that is used to
load class files.
2. Class (Method)Area:
Class (Method) Area stores per-class structures such
as the runtime constant pool, field and method data,
the code for methods.
3. Heap:
It is the runtime data area in which objects are
allocated.
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4. Stack:
Java Stack stores frames. It holds local variables and partial results, and plays a part in method
invocation and return.
Each thread has a private JVM stack, created at the same time as thread.
A new frame is created each time a method is invoked. A frame is destroyed when its method
invocation completes.
5. ProgramCounter Register:
PC (program counter) register. It contains the address of the Java virtual machine instruction
currently being executed.
6. Native Method Stack
It contains all the native methods used in the application.
7. Execution Engine:
a. A virtual processor
b. Interpreter: Read byte code stream then execute the instructions.
c. Just-In-Time (JIT) compiler: It is used to improve the performance. JIT compiles parts of the
byte code that have similar functionality at the same time, and hence reduces the amount of
time needed for compilation. Here the term? Compiler? Refers to a translator from the
instruction set of a Java virtual machine (JVM) to the instruction set of a specific CPU.

 Variable
Variable is name of reserved area allocated in memory.
 Local Variable
A variable that is declared inside the method is called local variable.
 Instance Variable
A variable that is declared inside the class but outside the method is called instance variable. It is not declared as
static.
 Static variable
A variable that is declared as static is called static variable. It cannot be local.
 Types of Variable
There are three types of variables in java
1. local variable
2. instance variable
3. static variable
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 DataTypes in Java
In java, there are two types of data types
1. Primitive data types
2. Non-primitive data types
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 Website: www.pskitservices.com
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 Advantage of naming conventions in java
By using standard Java naming conventions, you make your code easier to read for yourself and for
other programmers. Readability of Java program is very important. It indicates that less time is spent to
figure out what the code does.
Name Convention
Class name Should start with uppercase letter and be a noun e.g.
String , color Button, System, Thread etc.
interface name should start with uppercase letter and be an adjective
e.g. Runnable, Remote, Action Listener etc.
method name should start with lowercase letter and be a verb e.g.
action Performed(), main(), print(), println() etc.
variable name should start with lowercase letter e.g. first Name, order
Number etc.
package name should be in lowercase letter e.g. java, Lang, sql, until
etc.
constants name Should be in uppercase letter. e.g. RED, YELLOW,
MAX_PRIORITY etc.

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