Tutorials : Java by Example : Section 5 :

Objects and Classes

Introducing Classes and Objects

//Sourcecode import java.awt.*; import java.applet.*; //bubbles applet with a separate bubble class! class Bubble { //instance variables int x, y; Graphics g; //constructor public Bubble(int x, int y) { this.x=x; this.y=y; } public void drawRandomBubble(int x, int y) { int red=(int)(Math.random()*255); int green=(int)(Math.random()*255); int blue=(int)(Math.random()*255); Color randomColor=new Color(red, green, blue); g.setColor(randomColor); //generate a random number between 10 and 100 int diameter=(int)(Math.random()*90)+10; //make mouse cursor the center of our random bubble g.fillOval(x-diameter/2,y-diameter/2,diameter,diameter); } public void paint(Graphics gr) { g=gr; drawRandomBubble(x, y); } } public class Project23 extends Applet { Image Buffer; Graphics gBuffer; Bubble myBubble; public void init() { Buffer=createImage(size().width,size().height); gBuffer=Buffer.getGraphics(); } public boolean mouseDown(Event evt,int x,int y) { myBubble = new Bubble(x,y); myBubble.paint(gBuffer); repaint(); 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 classy bubbles!", 30,20); g.drawImage (Buffer,0,0, this); } }

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