JAVA OVERVIEW

Java

Originally from Sun Microsystem. Main components of Java:

Java Programming Language Programming language used to write software

for the Java Platform. Java API

Rich and fully featured class library. Java Platform

A range of runtime environments that support execution of software written in Java

Advantages of JAVA

Java is simple: Java was designed to be easy to use and is therefore easy to write, compile, debug, and learn than other programming languages. The reason that why Java is much simpler than C++ is because Java uses automatic memory allocation and garbage collection where else C++ requires the programmer to allocate memory and to collect garbage.

Java is object-oriented: Java is object-oriented because programming in Java is centered on creating objects, manipulating objects, and making objects work together. This allows you to create modular programs and reusable code.

Advantages of JAVA…

Java is platform-independent: One of the most significant advantages of Java is its ability to move easily from one computer system to another. 

The ability to run the same program on many different systems is crucial to World Wide Web software, and Java succeeds at this by being platform-independent at both the source and binary levels.

Java is distributed: Distributed computing involves several computers on a network working together. Java is designed to make distributed computing easy with the networking capability that is inherently integrated into it. 

Advantages of JAVA…

Writing network programs in Java is like sending and receiving data to and from a file. For example, the diagram below shows three programs running on three different systems, communicating with each other to perform a joint task.

Java is interpreted: An interpreter is needed in order to run Java programs. The programs are compiled into Java Virtual Machine code called bytecode. The bytecode is machine independent and is able to run on any machine that has a Java interpreter. With Java, the program need only be compiled once, and the bytecode generated by the Java compiler can run on any platform.

Advantages of JAVA…

Java is secure: Java is one of the first programming languages to consider security as part of its design. The Java language, compiler, interpreter, and runtime environment were each developed with security in mind.

Java is robust: Robust means reliable and no programming language can really assure reliability. Java puts a lot of emphasis on early checking for possible errors, as Java compilers are able to detect many problems that would first show up during execution time in other languages.

Advantages of JAVA…

Java is multithreaded: Multithreaded is the capability for a program to perform several tasks simultaneously within a program. In Java, multithreaded programming has been smoothly integrated into it, while in other languages, operating system-specific procedures have to be called in order to enable multithreading. Multithreading is a necessity in visual and network programming.

Java Platform

JVM Java Virtual Machine The emulation of a hardware device

JRE Java Runtime Environments Include core classes from the Java API. J2SE (Java 2 Platform, Standard Edition) J2EE (Java 2 Platform, Enterprise Edition) JSP (Java Server Pages) etc

Java Network Programming

Network clients Games Software agents Web applications Distributed systems.

Development Tools

Integrated Development Environments (IDE) Borland Jbuilder Symantec Visual Café Visual Age Visual J++ Kawa Blue J Notepad

Java System Development Kits (Java SDK)

Writing and Compiling JAVA Programs Setting the path and classpath

path=c:\jdk1.6.0_14\bin set classpath=C:\jsdk2_1-win\jsdk2.1;C:\

jswdk1_0_1-win\jswdk-1.0.1\lib;c:\jdk1.6.0_14\lib; C:\jdk1.6.0_14\jre\lib; C:\jdk1.6.0_14\jre\lib\ext; C:\TK6224 Network Programming\;

Write Programs Beware of file name and class name File name could have different class name. The JAVA compiler should produce class name. Class name is important file in running JAVA

programs

Writing and Compiling JAVA Programs… Compile

javac yourprograms.java If there are errors

Correct the error Compile the program once again

if there are no errors Make sure the class name. yourprograms.class (case sensitive)

Run java yourprograms Options are ready for expert users.

Writing and Compiling JAVA Programs… Different setting for Applet

javac yourapplet.java write html file for applet appletviewer or using web browser

Different setting for JAVA network programming Client Server – tomcat, client site, server site Socket Programming – socket in java Java Servlet – deal with database, JDBC RMI – rmic, rmiregistry, client, server,

yourprograms_STUB.class

Writing and Compiling JAVA Programs… JAVA Network Security

https Security API. Certificate Agents, Certificate Authority. Timestamp. SSL, SSH

Sample of Java Program

public class Fibonacci {

public static long fib(int n) {

if (n <= 1) return n;

else return fib(n-1) + fib(n-2);

}

public static void main(String[] args) {

int N = Integer.parseInt(args[0]);

for (int i = 1; i <= N; i++)

System.out.println(i + ": " + fib(i));

}

}

Sample of Java Program …

Compile Set the path and classpath. javac Fibonacci.java This produced Fibonacci.class

Run the program java Fibonacci

Very limited size of integer. Rewrite the program when deals with

bigger size of integer

Time is NOW

import java.util.*;public class Now { public static void main(String[] args) { Date now = new Date(); long nowLong = now.getTime(); System.out.println("Value is " +

nowLong); }}

Time IS NOW (Friendly Version)import java.util.*;import java.text.*;public class NowString { public static void main(String[] args) { Date now = new Date(); DateFormat df =

DateFormat.getDateInstance(); String s = df.format(now); System.out.println("Today is " + s); }}

Simple Applet

import java.awt.*;import java.applet.Applet;import java.awt.event.*;

public class randomDots extends Applet implements ActionListener{

Button drawButton;public void init() {

// create the button widgetdrawButton = new Button("Draw");

// add it to the applet guiadd(drawButton);

// register a listener for the buttondrawButton.addActionListener(this);

} // end of init

Simple Applet

public void paint( Graphics g ) {int x, y, r;for (int i=0; i < 5000; i++) {

// generate a random point to be the center of the circle// restrict it to beween 0 and 200 (the size of the applet window)x = (int) (Math.random()*400);y = (int) (Math.random()*400);

// select a random size of the radius (make it in the range 10..40)r = 10 + (int)(Math.random()*30);

// draw the circledrawCircle(g, x, y, r);

}} // end of paint

Simple Applet

private void drawCircle(Graphics g, int x, int y, int r) {// draws a circle at x,y of radius r in the graphics window g// chooses a random color for it as wellint red, green, blue;

// choose the rgb valuesred = (int) (Math.random() * 256);green = (int) (Math.random() * 256);blue = (int) (Math.random() * 256);

// set the foreground to the seledted colorg.setColor(new Color(red, green, blue));

// draw the ciclreg.fillOval(x-r, y-r, 2*r, 2*r);

} // end of drawCircle

Simple Applet

public void actionPerformed(ActionEvent e) {

// Nothing much to do here except repaint, for now

if (e.getSource() == drawButton)

repaint();

} // end of actionPerformed

} // end of applet

HTML File for Applet

<html><APPLET CODE="randomDots.class"

WIDTH=400 HEIGHT=400></APPLET></html>