Introduction to java

• Today Java , is one of the most popular programming
language which is used in critical applications like…

 web based applications
Embedded applications
 android mobile application.

Introduction

• Lets have a look in history of Java…
• Java was developed by James Gosling from Sun Microsystems in 1995.
• Introduced as an object-oriented language for general-purpose business
applications and for interactive, Web-based Internet applications.
• The goal was to provide platform-independent alternative to C++. In other
terms it is architecturally neutral, which means that you can use Java to
write a program that will run on any platform or device.
• Instead, Java runs on a Java Virtual Machine (JVM).

History & Evolution

• James Gosling ,Mike Sheridan and Patrick Naughton initiated the
green project in June 1991.
• Originally designed for small , embedded systems in electronic
appliances like set-top boxes.
• It was initially called as Oak and later on renamed as “Java” in 1995.
• Originally developed by James Gosling at Sun Microsystems in
1995.
• JDK 1.0 released in 1996.

History and Evolution

History of Java Releases
Java Version/Code Name

Release Date

Important Features/Code Name

JDK 1.0 (Oak)

23rd Jan 1996

Initial release

JDK 1.1

19th Feb 1997

Reflection , JDBC , Inner Classes
,RMI

J2SE 1.2 (Playground)

8th Dec 1998

Collection , JIT, String memory map

J2SE 1.3 (Kestrel)

8th May 2000

Java Sound , Java Indexing ,JNDI

J2SE 1.4 (Merlin)

6th Feb 2002

Assert , regex, exception chaining

J2SE 5.0 (Tiger)

30th Sept 2004

Generics ,autoboxing ,enums

Java SE 6.0 (Mustang)

11th Dec 2006

JDBC 4.0 , Java compiler API ,
Annotations

Java SE 7.0 (Dolphin)

28th July 2011

String in switch case ,exception
handling new way

Simple:
A Java programmer does not need to know the internal
functioning of Java, such as how memory is allocated to data.
Object-oriented:
Java supports the object-oriented approach to develop
programs.
Compiled and interpreted:
The Java programs are first compiled and then interpreted.
After the program is compiled, it is converted to a bytecode.
The Java Virtual Machine (JVM) then interprets this bytecode
into the computer code and runs it.
Portable:
Refers to the ability of a program to run on any platform without
changing the source code of a program.

Features of Java Environment

•

The following figure shows how the Java bytecode and the JVM together
make Java programs portable on different platforms.

Features of Java Environment

Distributed:
Java is designed for the distributed environment of the Internet
because it supports the various Internet protocols, such as
Transmission Control Protocols and Internet Protocol (TCP/IP).
Secure:
Java has built-in security features that verify that the programs
do not perform any destructive task, such as accessing the
files on a remote system.

Features of Java
Environment

• Java technology provides language part along with architecture for
running applications.
• Java Architecture provides
• Portable
• high-performance
• robust runtime environment.

• Various Components of Java Architecture are :
• Java Programming Language and class file
• JVM
• Java Application Programming Interface (API)

Java Architecture

• Java Runtime Environment contains JVM, class libraries and
other supporting components.
• Java source code is compiled into bytecode by Java compiler.
• This bytecode will be stored in class files.
• During runtime, this bytecode will be loaded, verified
and JVM interprets the bytecode into machine code which
will be executed in the machine in which the Java program
runs.

Java Runtime Environment (JRE)

• A Java Runtime Environment performs the following main
tasks respectively.
• Loads the class
• This is done by the class loader

• Verifies the bytecode
• This is done by bytecode verifier.

• Interprets the bytecode
• This is done by the JVM

Java Runtime Environment (JRE)

• Java programming language and class file:
• Java programs are saved with an extension, .java.
• A .java file is compiled to generate the .class file, which contains the
byte code.
• The JVM converts the byte code contained in the .class file to machine
object code.
• The JVM needs to be implemented for each platform running on a
different operating system.

Java Programming Lang. & Class file

• Its an abstract Machine forms the base of Java Platform.
• Specification that provides runtime environment in which java byte code
can be executed.
• Available for many hardware and software.

• JVM performs:
•
•
•
•

Loads code
Verifies code
Executes code
Provide Runtime Environment

Java Virtual Machine (JVM)

• Major Components of JVM
• Class Loader
• Byte code Verifier
• Just In Time (JIT) compiler

Java Virtual Machine

Interpreter
Byte
Code

Class
Loader

Byte code
Verifier

JIT Compiler

Java Runtime Environment

Java Virtual Machine

Running
Program

• Class Loader
• Class loader loads all the class files required to execute the
program.

• Byte code Verifier
•
•
•
•

Checks that code follows JVM specifications.
There is no unauthorized access to memory.
The code does not cause any stack overflows.
There are no illegal data conversions in the code such as float to
object references.

Components of JVM

• JIT Compiler
• Used to improve performance.
• It translates byte code only the first time.
• If repeated execution of code is required , it is automatically
mapped to the corresponding native machine code.
• JIT make use of the machine code which is cached and stored.

Components of JVM

Java Development Kit

• Package that provides the basic functionality of Java Language.
• Contains series of classes and methods

• Tools used to develop and execute java programs is known as JDK.
• It contains
•
•
•
•

Basic Tools( javac,java,javap,javadoc,appletviewer etc)
RMI tools (rmic,rmiregistry,rmid)
Security Tools (keytools,policytool etc.)
Java plug-in Tools

Basic Tools

Description

Javac

Compiler for java language

Java

Launcher of java application

Javadoc

API documentation generator

Appletviewer

Run and debug applets without a web
browser

Jar

Manage java archive files

Javap

Class file dissassembler

Java Development Kit

The Java API is a collection of software components that provide
capabilities, such as GUI.
The related classes and interfaces of the Java API are grouped
into packages.
The following figure shows how the Java API and the JVM forms
the platform for the Java programs on top of the hardware.

Java API

• Java can be used to develop more dynamic programs.
• Leading programming language for wireless technology and real time
embedded programming for cell phones.
• Major Categories of java programs :
• Applets
• Applications

Type of Java Programs

• Applets
• Small program embedded in a web page.
• Applets are downloaded over network and can make network
connections only to the host they are issued from.
• Graphical in nature and tends to contain controls like text field
, button label etc.

• Applications
•
•
•
•

Standalone programs written in java.
Invoked by using a JVM.
Can access the local file system.
Can execute on the server machine.

Types of Java Programs

• Temporary Path Setting
• Open command prompt
• Copy the path of bin folder
• Write in command prompt
• Set path=c:Program
FilesJavaJdk1.6.0_03bin;

• Permanent Path Setting
• Right click on My Computer
• Select Properties > Advanced tab >
Environment variables >new tab of
user variables > write path in
variable name > write path of bin
folder in variable value > ok

Setting Path for JDK in Windows

• Create a source document using any editor such as Notepad and save file as
.java
• For example: HelloWorld.java

• Compile the java file using “javac” command. Byte Code will be
generated on disk.

Javac HelloWorld.java

After Compilation

HelloWorld.class

• This byte code can run on any platform or device having JVM using

“java”
Command.

StepS are….

class simple
{
public static void main(String args[])
{
System.out.println(“Hello Java”);
}
}

To Compile : javac simple.java
To Run
: java simple

Sample Java Program

• class : Used to declare class in java.
• public : Access modifier which represents the visibility.
• static : Keyword for creating static method , so that we can access it
without creating object.
• void : Return type of main method , its doesn’t return anything.
• main : Represent the startup of the program
• String args[] : Used to store command line arguments.

Understanding Sample
Program

Source Code
Program

Compiler

Byte code

Compilation Process

Compilation & Execution

R
U
N
T
I
M
E

P
R
O
C
E
S
S

Class file

Class Loader

Byte Code Verifier

Interpreter

Runtime

Compilation & Execution

• Built-in support for multi-threading, socket communication, and memory
management (automatic garbage collection).
• Object Oriented (OO).
• Better portability than other languages across operating systems.
• Supports Web based applications (Applet, Servlet, and JSP) .
• Supports distributed applications (sockets, RMI, EJB etc.) and network
protocols (HTTP, JRMP etc.) with the help of extensive standardized
APIs (Application Programming Interfaces).

Advantages of Java Programming
Language

Introduction to java

In this document

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