/** 
*實現下雪，原理是利用線程讓雪花移動 
**/ 
import java.awt.* ; 

public class Snow{ 
public static void main(String args[]) { 
Frame w = new Frame() ; 
w.setSize(1024 , 768) ; 
w.setBackground(Color.black) ; 

MyPanel mp = new MyPanel() ; 
w.add(mp) ; 

Thread t = new Thread(mp) ; 
t.start() ; 

w.show() ; 
} 
} 

class MyPanel extends Panel implements Runnable{ 

int x[] = new int[300] ; 
int y[] = new int[300] ; 

MyPanel() { 
for (int i = 0; i<300; i++) { 
x[i] = (int)(Math.random()*1024) ; 
y[i] = (int)(Math.random()*768) ; 
} 
} 

public void paint(Graphics g) { 
g.setColor(Color.white) ; 

for (int i = 0; i<300; i++) { 
g.drawString("*" , x[i] , y[i]) ; 
} 
} 

public void run() { 
while(true) { 
for (int i = 0; i<300; i++) { 
y[i] ++ ; 
if(y[i]>768){ 
y[i] = 0 ; 
} 
} 

try { 
Thread.sleep(20) ; 
 } 
 catch (Exception ex) { 
 } 

repaint() ; 

} 
} 
}