【例 11-18】小应用程序设置了一个文本区，用于记录一系列鼠标事件。当鼠标进入小应用程序窗口时，文本区显示“鼠标进来”；当鼠标离开 窗口时，文本区显示“鼠标走开”；当鼠标被按下时，文本区显示“鼠标按下”，当鼠标被双击时，文本区显示“鼠标双击”；并显示鼠标的坐标。程序还显示一个红色的圆，当点击鼠标时，圆的半径会不断地变大。
import java.applet.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class MyPanel extends JPanel{
    public void print(int r){
        Graphics g = getGraphics();
        g.clearRect(0,0,this.getWidth(),this.getHeight());
        g.setColor(Color.red);
        g.fillOval(10,10,r,r);
    }
}
class MyWindow extends JFrame implements MouseListener{
    JTextArea text;
    MyPanel panel;
    int x,y,r =10;
    int mouseFlg=0;
    static String mouseStates[]={"鼠标键按下","鼠标松开","鼠标进来","鼠标走开","鼠标双击"};
    MyWindow(String s){
        super(s);
        Container con = this.getContentPane();
        con.setLayout(new GridLayout(2,1));
        this.setSize(200,300);
        this.setLocation(100,100);
        panel = new MyPanel();
        con.add(panel);
        text = new JTextArea(10,20);
        text.setBackground(Color.blue);
        con.add(text);
        addMouseListener(this);
        this.setVisible(true);
        this.pack();
    }
    public void paint(Graphics g){
        r = r+4;
        if(r>80){
            r=10;
        }
        text.append(mouseStates[mouseFlg]+"了，位置是：" +x+","+y+"\n");
        panel.print(r);
    }
    public void mousePressed(MouseEvent e){
        x = e.getX();
        y = e.getY();
        mouseFlg = 0;
        repaint();
    }
    public void mouseRelease(MouseEvent e){
        x = e.getX();
        y = e.getY();
        mouseFlg = 1;
        repaint();
    }
    public void mouseEntered(MouseEvent e){
        x = e.getX();
        y = e.getY();
        mouseFlg = 2;
        repaint();
    }
    public void mouseExited(MouseEvent e){
        x = e.getX();
        y = e.getY();
        mouseFlg = 3;
        repaint();
    }
    public void mouseClicked(MouseEvent e){
        if(e.getClickCount()==2){
            x = e.getX();
            y = e.getY();
            mouseFlg = 4;
            repaint();
        }
        else{}
    }
}
public class Example6_8 extends Applet{
    public void init(){
        MyWindow myWnd = new MyWindow("鼠标事件示意程序");
    }
}