import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class ball extends JPanel implements KeyListener{
                private int x = 20;//小球的大小
                private int y = 20;//小球的大小
                private int a = 50;//小球的位置
                private int b = 50;//小球的位置
                private int x1 = 200;//窗体的大小
                private int y1 = 200;//窗体的大小
    ball(){
        JFrame jf = new JFrame();
        jf.setLocation(200,200);
        jf.setSize(x1,y1);
        JPanel p1 = new p();//覆盖组建的paint方法才能用
        jf.getContentPane().add(p1);
        jf.setVisible(true);
        jf.addKeyListener(this);
        try{ 
            while(true){
                Thread.sleep(50);
                p1.repaint();
                }
            }catch(InterruptedException e){
                e.printStackTrace();
            }
        }
    
    
    public void keyTyped(KeyEvent e){

    }
    public void keyPressed(KeyEvent e){
        //System.out.println(e.getKeyCode());
        //System.out.println(e.VK_KP_DOWN);

        if(e.getKeyCode() == 40){//下

                y += 4;            
        }
        if(e.getKeyCode() == 39){//右
                if(x>=x1-(x-b/2)){//请问怎么计算小球撞到窗体边缘.我感觉老是不行帮我鲁下思路吧高人
                        
                }else{
                x += 4;            
                }    
        }
        if(e.getKeyCode() == 37){//左
                x -= 4;            
        }
        if(e.getKeyCode() == 38){//上
                y -= 4;            
        }
    }
    public void keyReleased(KeyEvent e){
        //System.out.println("+++++++++++++++");
    }

    public static void main(String[] args){
        ball b = new ball();
        
        //b.paint();
        }
                private class p extends JPanel{
                    public void paint(Graphics g){
                        super.paint(g);   
                        g.setColor(Color.blue);
                        //System.out.println(a +"a"+ b+"b" + x +"x"+ y+"y");
                        g.fillOval(x,y,a,b);
                        g.drawOval(x,y,a,b);
                        
                    }
            }
}