Java overview

1. Java overview

2. 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

3. 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.

4. 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. 

5. 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.

6. 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.

7. 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.

8. 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

9. Java Network Programming • Network clients • Games • Software agents • Web applications • Distributed systems.

10. 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)

11. 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

12. 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.

13. 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

14. Writing and Compiling JAVA Programs… • JAVA Network Security • https • Security API. • Certificate Agents, Certificate Authority. • Timestamp. • SSL, SSH

15. 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)); } }

16. 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

17. 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); } }

18. Time IS NOW (Friendly Version) import java.util.*; import java.text.*; public class NowString { public static void main(String[] args) { Date now = new Date(); DateFormatdf = DateFormat.getDateInstance(); String s = df.format(now); System.out.println("Today is " + s); } }

19. 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

20. Simple Applet public void paint( Graphics g ) { int x, y, r; for (inti=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

21. 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 seledtedcolor g.setColor(new Color(red, green, blue)); // draw the ciclre g.fillOval(x-r, y-r, 2*r, 2*r); } // end of drawCircle

22. 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

23. HTML File for Applet <html> <APPLET CODE="randomDots.class" WIDTH=400 HEIGHT=400> </APPLET> </html>