15.7

 

import java.awt.*;
import java.util.Scanner;

import javax.swing.*;

public class Test extends JFrame{
    
    public Test(){
        setLayout(new GridLayout(3,3,0,0));
        
        for(int i = 0; i < 9; i++)            
        add(new WellPanel((int) Math.round(Math.random()*2)));
    }
    
    public static void  main(String[] args){    
        Test frame = new Test();
        frame.setSize(400, 400);
        frame.setTitle("Exercise15_7");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null); // Center the frame
        frame.setVisible(true);        
    }
}

class WellPanel extends JPanel{
    public static final int EMPTY = 0;
    public static final int CIRCLE = 1;
    public static final int FORK = 2;
    private int type = 1;
        
    public WellPanel(int type){
        this.type = type;
    }
    
    protected void paintComponent(Graphics g){
        super.paintComponent(g);
        
        switch(type)
        {
        case EMPTY:  break;
        case CIRCLE: g.drawOval(0,0,getWidth()-10, getHeight()-10); break;
        case FORK: g.drawLine(0, 0, getWidth()-10, getHeight()-10);g.drawLine(0, getHeight()-10, getWidth()-10,0); break;
        }
    }
    
    public Dimension getPreferredSize() {
        return new Dimension(80, 80);
      }
}

下面是效果图：