963.introduction to java

8/7/2019 963.Introduction to Java

1/15

Introduction to JAVA


2/15

What is JAVA?

JAVA technology is both a programming languageand a platform.

The Java programming language is the language in

which Java applications, applets, servlets, andcomponents are written.

The Java platform is the predefined set of Javaclasses that exist on every Java installation; theseclasses are available for use by all Java programs.

The Java platform is also sometimes referred to asthe Java runtime environment or the core Java APIs(application programming interfaces).


3/15

History of Java

B leads to C evolved into C++ sets the stages for Java

In 1990, Sun Microsystems began a project called GreenProject to develop software for consumer electronics.James Gosling, a veteran engineer was assigned to thenew Green Project.

Gosling began writing software in C++ for embedding intosuch items as toasters, VCRs etc. But soon he realized thatC++ was the wrong tool for the job as it is susceptible tobugs that can crash the system. Goslings solution to theproblems of C++ was a new language called Oak.


4/15

Oak preserved the familiar syntax of C++ butomitted the potentially dangerous features

like explicit resource references, pointerarithmetic and operator overloading, etc.

When the World Wide Web became popularin 1994, Sun realized that Oak was the

perfect programming language for the Web.Thus in 1994, they completed work on aproduct known as Web Runnerwas laterrenamed as Hot Java. Finally, in 1995, Oak

was renamed Java and the team announcedthat the Netscape Navigator Internet browserwould incorporate Java technology.


5/15

Features of Java

Simple

Architecture Neutral

compiler loader

.cpp

C++ Compilation Process

javac JIT

(JVM)

Java Compilation Process

Source Code

.cpp .exe.obj

Native Code.class

fileSource Code

.java


6/15

Object Oriented Robust

Secure

Multithreaded

Distributed

Dynamic

Automatic Memory Management and

Garbage Collection


7/15

Advantages of Java

Simple

Fewer bugs and reusable code

We need to write less code

Avoid platform dependencies. (Write once,run everywhere)

Automatic version check


8/15

Windows/Pentium

System

UNIX

System

SERVER

Class FilesContaining

Bytecodes

Class Loader

Bytecode Verifier

JIT

Class Loader

Bytecode Verifier

JIT

UNIX system

machine levelinstructions(native code)

Pentium system

machine levelinstructions

(native code)

(JVM)

NETWORK

Working of Java


9/15

Additional class

files needed by the

program may be

stored on disk ornetwork

Main Program

consisting of Java

bytecode in a

class file

Class Loader

Bytecode Verifier

Execution Unit

JVM

Embedded in

Browser

Client System

Internet

Server

Server

Working of JAVA on Internet


10/15

JAVA Platform, JDK, JRE

Java Platform A platform is a h/w or s/w environment inwhich a program runs. Most platforms can be describedas a combination of the operating system and underlyingarchitecture. The Java platform differs from others in thatits a s/w only platform that runs on the top of other h/w

based platforms. JDK Java Development toolKit is a bundle of s/w to

develop java based applications.

JRE Java Runtime Environment is an implementationof JVM to execute java programs. JRE consists of twocomponents:

JVM

The Java Application Programming Interface (API)


11/15

JVM Java Virtual Machine

a virtual machine (VM) is a s/w implementation of a

machine (computer) that executes programs like a realmachine.

A .class file does not contain code that is native toour processor. It instead contains bytecodes themachine language of the JVM. The Java launcher tool

then runs our application with an instance of the JVM.Because the JVM is available on many differentoperating systems, the same .class files are capableof running on different platforms.

API the API is a large collection of readymade s/w componentsthat provide many useful capabilities. It is grouped intolibraries of related classes and interfaces ; these librariesare known as packages.


12/15

Steps to createand executea Java

program Creating a program using an editor

Compiling a Java Program into Byte codes

Loading a Program into Memory

Byte code Verification

Execution


13/15


14/15

Java Versions & Environments

Till now Java has undergone three significant versionchanges.

It was first launched as Java 1.0, which is stillextensively supported by a majority of browsers.

Then came Java 1.1, which had a languageenhancements, an improved user interface, andevent handling.

Finally Sun has come up with the latest version as

Java 1.2.2 which it callsJava 2.

Java is available in many environments. Javasoftware is most easily available as JDK (JavaDevelopment Toolkit) version 1.0, 1.1 or 1.2.


15/15

There are many other development

e

nvi

ronme

nts for Jav

a.Some of them are:

Java Workshop

Borland Jbuilder

Symantec Visual Caf

Visual Java (VJ++)

Supercede etc.

963.introduction to java

Documents