Tutorials : Java by Example : Section 5 :

Objects and Classes

Introducing Classes and Objects

//Sourcecode import java.awt.*; import java.applet.*; class BreathingBubble { //instance variables int x, y, diameter, startDiameter, endDiameter; boolean growing=true; Color randomColor; Graphics g; //constructor public BreathingBubble() { int red=(int)(Math.random()*255); int green=(int)(Math.random()*255); int blue=(int)(Math.random()*255); //each bubble object has one random color randomColor=new Color(red, green, blue); //start diameter between 10 and 30 startDiameter=(int)(Math.random()*20)+10; //end diameter between 50 and 150 endDiameter=(int)(Math.random()*100)+50; diameter=startDiameter; } public void setPosition(int x, int y) { this.x=x; this.y=y; } public void drawBubble() { g.setColor(randomColor); g.fillOval(x-diameter/2,y-diameter/2,diameter,diameter); } public void breathe() { //grow till end diameter is reached if(growing) { if(diameter<endDiameter) diameter++; else growing=false; } //shrink till start diameter is reached else { if(diameter>startDiameter) diameter--; else growing=true; } } public void paint(Graphics gr) { g=gr; drawBubble(); } } public class Project25 extends Applet implements Runnable { Image Buffer; Graphics gBuffer; BreathingBubble myBubble[]; Thread runner; boolean clicked; int index; int MAX=100; public void init() { Buffer=createImage(size().width,size().height); gBuffer=Buffer.getGraphics(); myBubble = new BreathingBubble[MAX]; } public void start() { if (runner == null) { runner = new Thread (this); runner.start(); } } public void stop() { if (runner != null) { runner.stop(); runner = null; } } public void run() { Thread.currentThread().setPriority(Thread.MAX_PRIORITY); while(true) { try {runner.sleep(15);} catch (Exception e) { } //bubble methods may only be accessed, if we have //created the object in the mouseDown method! if(clicked) { for(int i=0;i<index;i++) { myBubble[i].breathe(); myBubble[i].paint(gBuffer); } } repaint(); } } public boolean mouseDown(Event evt,int x,int y) { if(index<MAX) { myBubble[index] = new BreathingBubble(); myBubble[index].setPosition(x,y); index++; } clicked=true; return true; } public void update(Graphics g) { paint(g); } public void paint(Graphics g) { gBuffer.setColor(Color.black); gBuffer.drawString("Click the applet to paint breathing bubbles!", 20,20); g.drawImage (Buffer,0,0, this); //paint the background white (must be done last!) gBuffer.setColor(Color.white); gBuffer.fillRect(0,0,size().width,size().height); } }

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