16.7

import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.*;

public class Test_16_7 extends JFrame{
    private JP j1 = new JP();
    public Test_16_7(){
        j1.addMouseListener(new MouseAdapter()
                {
            public void mousePressed(MouseEvent e)
            {
                j1.color = Color.BLUE;
                j1.repaint();
            }
            public void mouseReleased(MouseEvent e)
            {
                j1.color = Color.RED;
                j1.repaint();
            }
                });
        add(j1);
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Test_16_7 T1 = new Test_16_7();
        T1.setTitle("Test_16.7");
        T1.setSize(200,200);
        T1.setLocationRelativeTo(null);
        T1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        T1.setVisible(true);
    }

    
    class JP extends JPanel{
        Color color = Color.BLACK;
        
        protected void paintComponent(Graphics g){
            super.paintComponent(g);
            
            g.setColor(color);
            g.fillRect(0, 0, getWidth(), getHeight());
        }
    }
}

效果图：