●プログラム・リスト●

import java.awt.*;
import java.awt.event.*;

public class Test12 extends Frame implements ActionListener,Runnable {
    MyCanvas c1;
    Button b1;
    Thread t1;
    int lastX,lastY,moveX,moveY;
        
    public Test12() {
        super();
        setTitle("Hello");
        setSize(300,250);
        setLayout(null);
        
        c1 = new MyCanvas();
        c1.setBounds(25,25,250,150);
        this.add(c1);
        
        b1 = new Button("GO");
        b1.setBounds(25,200,100,25);
        b1.addActionListener(this);
        this.add(b1);
    }
        
     public static void main (String args []) {
        new Test12().setVisible(true);
    }
        
    public void actionPerformed(ActionEvent ev) {
        if (ev.getSource() == b1) {
            moveX = (int)(Math.random() * 21 - 11);
            moveY = (int)(Math.random() * 21 - 11);
            if (t1 == null){
                t1 = new Thread(this);
                t1.start();
            }
        }
    }
        
    public void run(){
        try {
            lastX = 0;
            lastY = 0;
            while(true){
                if (lastX + moveX < 0 || lastX + moveX > c1.getWidth()){
                    moveX *= -1;
                }
                if (lastY + moveY < 0 || lastY + moveY > c1.getHeight()){
                    moveY *= -1;
                }
                lastX += moveX;
                lastY += moveY;
                c1.repaint();
                t1.sleep(100);
            }
        } catch(Exception e){
            System.out.println(e);
        }
    }
        
    class MyCanvas extends Canvas{

        public void paint(Graphics g){
            g.setColor(Color.blue);
            g.fillOval(lastX - 10,lastY - 10,20,20);
        }
    }
}