java -an overview

8/7/2019 JAVA -an overview

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Java - An Introduction

Java - The new programming language fromSun Microsystems

Java -Allows anyone to publish a web pagewith Java code in it

Java - CPU Independent language

Java - James , Arthur Van , and others

Java -The name that survived a patent

search Oak -The predecessor of Java

Java is C++ -- ++


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Java as Object Oriented

Objects all the way down

Simple and Familiar: C++ Lite

No Pointers! Dynamic Binding

Single Inheritance with Interfaces


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According to Sun, Java is...

Simple and PowerfulSimple and Powerful Object OrientedObject Oriented

PortablePortable

Architecture NeutralArchitecture Neutral

DistributedDistributed

MultiMulti--threadedthreaded

Robust, Secure/SafeRobust, Secure/Safe

InterpretedInterpreted

High PerformanceHigh Performance

DynamicDynamic pogrammingpogramming language/platform.language/platform.


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Total Platform Independence

JAVA COMPILERJAVA COMPILER

JAVA BYTE CODEJAVA BYTE CODE

JAVA INTERPRETERJAVA INTERPRETER

Windows 95 Macintosh Solaris Windows NT

(translator)

(same for all platforms)

(one for each different system)


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Java Virtual Machine

Must Run on Any Architecture

Program

in JavaJava

Compiler

Java

Bytecode

Java Virtual Machine

WRITE ONCE, RUN ANYWHERE!

debug

pretty portable


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Why Java?

Its the current hot language

Its entirely object-oriented

It has a vast library of predefined objectsand operations

Its more platform independent

this makes it great for Web programming Its more secure

It isnt C++


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Java in the World ofDistributed Computing

Class Loader

Lightweight Binary Class Files

Multithreading Dynamic

Good communication constructs

Secure


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Object Oriented Languages-a Comparison

Feature C++Objective

C Ada Java

Encapsulation Yes Yes Yes Yes

Inheritance Yes Yes No YesMultiple Inherit. Yes Yes No No

Polymorphism Yes Yes Yes Yes

Binding (Early/Late) Both Both Early Late

Concurrency Poor Poor Difficult YesGarbage Collection No Yes No Yes

Genericity Yes No Yes No

Class Libraries Yes Yes Limited Yes


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Java better than C++ ?

No Typedefs, Defines, or Preprocessor

No Global Variables

No Goto statements No Pointers

No Unsafe Structures

No Multiple Inheritance No Operator Overloading


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So Whats Java Good For?

Java Applet

Server

Java Applet


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11

The Java programming

environment Java programming language specification Syntax of Java programs

Defines different constructs and their semantics

Java byte code: Intermediate representation for Java programs

Java compiler: Transform Java programs into Java byte code

Java interpreter: Read programs written in Java byte code and execute

them

Java virtual machine: Runtime system that provides various services

to running programs

Java programming environment: Set of libraries that provide services

such as GUI, data structures,etc.

Java enabled browsers: Browsers that include a JVM + ability to load

programs from remote hosts


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Applets, Servlets and

Applications An appletis designed to be embedded in a

Web page, and run by a browser

Applets run in a sandboxwith numerousrestrictions; for example, they cant readfiles and then use the network

A servletis designed to be run by a webserver

An application is a conventional program


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Java on the Web: Java Applets

Clients download applets via Web browser Browser runs applet in a Java Virtual

Machine (JVM)

Interactive web, security, and client consistency

Slow to download, inconsistent VMs (besides,

flash won this war)

Applet

ClientServer


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Java on the Web: J2EE

Thin clients (minimize download) Java all server side

ClientServer

JSPs

Servlets

EJB

JDBC


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Applets and GUI


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AWT & Applets

An Applet is a Java program capable of running from within a web page(HTML document)

Steps to incorporate and run an applet:

Have MyApplet.java

javac MyApplet.java

Have MyApplet.class Create MyApplet.html

appletviewer MyApplet.html (or open MyApplet.html in browsers like

Netscape/IE).


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Applet methods

Unlike Applications, Applets do not have

main().

Instead, they have : init(), start(), stop(),

paint(), update(), repaint(), destroy().

All methods need not be implemented -- there

are default versions for all of them.

AppletContext Applet derived from AWT Panel

Hooks into Browser environment

Can be used to link to another Web page


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Multithreading in Java(A built-in feature in Java)


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Single and MultithreadedProcesses

Single-threaded Process

Single instruction stream Multiple instruction stream

Multiplethreaded Process

Threads of

Execution

Common

Address Space

threads are light-weight processes within a process


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Thread states

new

runnable non-runnable

dead

wait()

sleep()

suspend()

blocked

notify()slept

resume()

unblocked

start()

stop()


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Threading Mechanisms...

Create a class that extends the Thread class

Create a class that implements the Runnable interface


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Server

Threads

Message Passing

Facility

Server Process

Client Process

Client Process

User Mode

Kernel Mode

Threads in Action...

Multithreaded Server


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Just to Summarize

Java as a Comprehensive Programming

Solution

Object Oriented Portable

High Performance

Geared for Distributed Environments

Secure

Highly suitable for Internet programming


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Java is really very well poised

Incredible leverage from the Web

Will impact the C++ and Smalltalk markets Rate of progress is astonishingly high

Development environments

CORBA linkages Components


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java -an overview

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