CS335 Graphics and Multimedia

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1 CS335 Graphics and Multimedia Fuhua (Frank) Cheng Department of Computer Science University of Kentucky Lexington, KY

2 -2-1. Programming Using JAVA JAVA history: WHY JAVA? Simple Objected-oriented Supports the internet Platform-independent Robust Many safety features Multithreading Has powerful libraries

3 -3- JAVA systems Java development environment Java language Java applications programming interface (API) The Jav a Development Environment Early version: JDK: Sun Java Developer s Kit, Version 1.2 Current version J2SE: Java 2 Platform, Standard Edition J2EE: Java 2 Platform, Enterprise Edition J2ME: Java 2 Platform, Micro Edition javac java appletviewer jdb compiler interpreter for a java application interpreter for a Java applet debugger

4 -4- Development Cycles Edit Compile Load Verify Ececute (Java is interpreted) A. Editing source code Source code is saved inafile with a.java extension. Java looks like C++. B. Compiling source: javac Welcome.java produces "bytecode" file: Welcome.class C. Loading Class loader puts compiled code (bytecodes) into memory Bytecode Verifier verifies that codes are valid and legal (things like address spaces, etc.)

5 -5- (In an internet environment, the loader can 1. Load code into the local machine 2. Ship code to another machine and load it there Cases 1 and 2 lead to the idea of applet versus standalone Java programs (applications): applet : Java code designed to run in a World Wild Web browser (can be shipped across a network and loaded on a remote machine). applications: java code stored and executed from the user s local machine.

6 -6- D. Executing a compiled Java program A stand-alone application calls the Java interpreter: java Welcome (no extension; assumes.class) Loader finds Welcome.class, loads it into local memory, verifies it, and interprets (executes) it.

7 -7- An applet uses HTML through the appletviewer command, or using an IE or Netscape browser. Inthe first case appletviewer test.html where test.html is an html file with the applet tag: <! test.html > <HTML> <HEAD> <TITLE> An applet Example </TITLE> </HEAD> <BODY> <APPLET CODE = "Welcome.class" width=275 height=55> </APPLET> </BODY> </HTML> In this case, the applet code is obtained through the HTTP protocol prior to the load. (The VERIFY step is different in this case!)

8 -8- Example: Standalone program (application) import java.io.*; public class Average { public static void main( String args[] ) throws IOException { int count = 0; while ( count <= 10 ) { System.out.println("counter is " + count ); count++; Notes: - Noapplet class - Flow ofcontrol always starts in main()

9 Example: Applet -9- import java.applet.applet; import java.awt.graphics; public class Welcome extends Applet { public void paint( Graphics g ) { g.drawstring("welcome to Java!", 25, 25 ); Notes: - Execution in an applet always starts with the init method, then the start method, and finally the paint method. These three calls start every applet s execution; there is no main. - Applet is called the superclass (base class), and Welcome is called the subclass (derived class).

10 Java Class -10- Java programs are built from Classes A Class is an object definition, includes data (fields) and functions (methods) on that data: public class MyCourseGrade { int prog1; int prog2;.. int final_exam; computeaverage() {.. { Class : Object : Java program : code which defines an object avariable (data + methods) which is an instance of a class abunch of class definitions, variables, etc.

11 -11- One special class (the "mother of all classes") contains main(), and this is where flow ofcontrol begins: class Motherclass main ( ) Kernel of execution class anyclass member methods 1 member methods 2 Notes: Java flow of control starts in main(), in whichever class it is defined in There can only be one class per file (unless you are defining subclasses) The filename must match the class name in a Java source file!

12 Example 1: -12- A Java program with one class and one member called main(). import java.io.*; public class Test { public static void main( String args[] ) throws IOException { System.out.println( "That s it, folks!" ); Scopes (a class s data and methods) Data (none defined) Member functions main()

13 Example 2: -13- Add another member function. import java.io.*; public class Test { public static void main( String args[] ) throws IOException { System.out.println( "That s it, folks!" ); public void dostuff() { System.out.println( "I m doing stuff." ); Example 2, Scopes Data (none defined) Member functions main() dostuff()

14 Example 3: -14- Define an object of class "Test" and make a function call import java.io.*; public class Test { public static void main( String args[] ) throws IOException { Test t; // t is of type "Test" t=new Test(); // allocate object t.dostuff(); // call member function System.out.println( "That s it, folks!" ); public void dostuff() { System.out.println( "I m doing stuff." );

15 -15- Notes Static methods cannot access nonstatic class members directly (which is why "t" is defined as above). "main()" must always be static (A static method exists even when a class has not been instantiated; i.e., independent of any objects of that class)

16 Example 4: -16- Put main class and a different class in separate files. //Test.java import java.io.*; public class Test { public static void main( String args[] ) throws IOException { Stuff t; //tisoftype "stuff" t=new Stuff(); // allocate object t.dostuff(); // call member function System.out.println( "That s it, folks!" );

17 -17- //Stuff.java public class Stuff { public void dostuff() { System.out.println( "I m doing stuff." ); Notes One class per file Tocompile: javac Test.java (The compiler finds the other files automatically!)

18 -18- What about "applets?" There is no main() ;why not? Where are the parameters coming from (in the so-called "paint" methods, for example)? Answers The "Applet" class contains a "main()" method, but you don t see it (it is in the appletviewer and the web browser). You need only write other methods, once you see how the pre-defined main() would invoke them, to set up and run things. Applet s main method calls "init" method, then "start" method, then "paint" method, etc. The programmer just manipulates these: "paint" method draw stuff togui "action" method handle events

19 Applet Example //Welcome.java import java.applet.applet; import java.awt.graphics; -19- public class WhoWin extends Applet implements ActionListener { Label prompt; Te xtfield input; public void init() { prompt = new Label("Who is going to win?"); add( prompt ); input = new TextField( 20 ); add( input ); input.addactionlistener( this ); public void paint( Graphics g ) { g.drawstring( "(Input team name)", 250, 50 ); public void actionperformed( ActionEvent e ) { showstatus(e.getactioncommand());

20 -20- Scope of an applet (stuff you don t see) data various methods Above example s scope prompt input init() paint() ActionPerformed() Notes A non-static member function can call another member function without using the "object.method" notation (as in the "add" call). Note how this is different from "main". Applet is just an extensively robust and rich class, most of which is hidden. In particular, its "main" is hidden. All applets must inherit from the Applet class.

21 Java I/O -21- Applet class provides ways to manage I/O on the "GUI". System object provides a way to manage I/O from a more traditional "stream" (terminal window). Applet-based I/O requires the "action()" method to deal with GUI mouse events. System object requires no action() method. But terminal I/O is inadequate in a browser-based (GUI) environment.

CS 335 Graphics, Image Processing, User Interface Design

CS 335 Graphics, Image Processing, User Interface Design 2-3:15 TR 207 RGAN Brent Seales 1 Course Goals Programming with Java and associated APIs Graphical User Interfaces (GUIs) Introduction to Image