Download Overview on Java Programming Languange

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
 Java
A
and fully featured class library.
Platform
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_1win\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 widget
drawButton = new Button("Draw");
// add it to the applet gui
add(drawButton);
// register a listener for the button
drawButton.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 circle
drawCircle(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 well
int red, green, blue;
// choose the rgb values
red = (int) (Math.random() * 256);
green = (int) (Math.random() * 256);
blue = (int) (Math.random() * 256);
// set the foreground to the seledted color
g.setColor(new Color(red, green, blue));
// draw the ciclre
g.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>