Tutorials : Java by Example : Section 7 :

Now let's have some real fun with falling letters! We create a class FallingCharacter that represents the falling letters. We create an array of objects of that class (here: 100, represented by the variable MAX, can be changed easily). Each object takes care for random values for the initial position, size, color and speed! The speed is represented by the double precision floating point variable yinc, which is added to the y position in the member method fall(). Only floating point variables guarantee for smooth movement in many different speed values. They are casted to int values only in the paint method, in the end. The constructor of the FallingCharacter class receives the width and height of the applet as parameters, to make it possible to easily change the applet size without changing the code. After reaching the bottom of the window, the letters reappear at the top again.

//Sourcecode import java.awt.*; import java.applet.*; class FallingCharacter { int fontSize, h; double x, y, yinc; String s, alphabet="ABCDEFGHIJKLMNOPQRSTUVWXYZ"; Color color; Graphics g; Font font; public FallingCharacter(int width, int height) { h=height; //random font size 10..50 fontSize=(int)(Math.random()*40)+10; font=new Font("TimesRoman", Font.PLAIN, fontSize); //random font color int red=(int)(Math.random()*255); int green=(int)(Math.random()*255); int blue=(int)(Math.random()*255); color=new Color(red, green, blue); //random initial coordinates within the applet bounderies x=(Math.random()*width); y=(Math.random()*height); //random falling speed yinc=(Math.random()*2.5)+1.0; //random substring from the alphabet string (one out of 26 characters) int character=(int)(Math.random()*26); s=alphabet.substring(character, character+1); } public void fall() { if(y<h+fontSize) y+=yinc; else y=-fontSize; } public void paint(Graphics gr) { g=gr; g.setColor(color); g.setFont(font); g.drawString(s,(int)x,(int)y); } } public class Project38 extends Applet implements Runnable { Thread runner; Image Buffer; Graphics gBuffer; int i; static final int MAX=100; FallingCharacter fc[]; public void init() { //create graphics buffer, the size of the applet Buffer=createImage(size().width,size().height); gBuffer=Buffer.getGraphics(); fc = new FallingCharacter[MAX]; for(i=0;i<MAX;i++) fc[i] = new FallingCharacter(size().width-30,size().height); } 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() { while(true) { Thread.currentThread().setPriority(Thread.MAX_PRIORITY); try {runner.sleep(15);} catch (Exception e) { } repaint(); } } public void drawStuff() { gBuffer.setColor(Color.black); gBuffer.fillRect(0,0,size().width,size().height); for(i=0;i<MAX;i++) fc[i].fall(); for(i=0;i<MAX;i++) fc[i].paint(gBuffer); } public void update(Graphics g) { paint(g); } public void paint(Graphics g) { drawStuff(); g.drawImage (Buffer,0,0, this); } }

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