myblackball.java

JavaExample

//================== MyBlackBall.java =====================
//import java.applet.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.event.*;
public  class MyBlackBall
extends JFrame implements ActionListener
  {
  Timer timer;
  private int d=30;
  private int x=-1;
  private int y=-1;
  private int dx=2;
  private int dy=2;
  private int appWidth=0;
  private int appHeight=0;
  public MyBlackBall()
    {
       super("乱七八糟");
       setSize(500,320);
    show();
    appWidth=this.getSize().width;
    appHeight=this.getSize().height;
    setBackground(Color.yellow);
    }
  public void start()
    {
    timer = new Timer(20, this);
    timer.start();
    }
  public void actionPerformed(ActionEvent e)
    {
    repaint();
    }
  public void paint(Graphics g)
    {
    g.setColor(Color.black);
    Rectangle r = g.getClipBounds();
    g.clearRect(r.x, r.y, r.width, r.height);
    appWidth=this.getSize().width;
    appHeight=this.getSize().height;
    x=x+dx;
    y=y+dy;
    if (x > (appWidth-d) | x<-1) dx=-dx;
    if (y > (appHeight-d) | y<-1) dy=-dy;
    g.fillOval(x, y, d,d);
    }
 
  }