//cd c:\JavaTry\MySwing
//javac ColorTest4.java
//set CLASSPATH=.	
//appletviewer ColorTest4.java

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/*
    <applet code="ColorTest4.class" width=400 height=300>
    </applet>
*/

public class ColorTest4 extends JApplet implements ActionListener {
    JPanel panel;
    public void init(){
        Container contentPane = getContentPane();
        panel = new JPanel();
        JButton yellow = new JButton("Yellow");
        JButton blue = new JButton("Blue");
        JButton red = new JButton("Red");
 
        panel.add(yellow);
        panel.add(blue);
        panel.add(red);
        contentPane.add(panel);

        yellow.addActionListener(this);
        blue.addActionListener(this);
        red.addActionListener(this);
    }
 
   public void actionPerformed(ActionEvent event) {
        Color c;
        String source = event.getActionCommand();
        if (source == "Yellow") {
            c=Color.yellow;
        } else if  (source == "Blue") {
            c=Color.blue;
        } else  {
            c=Color.red;
        }
        panel.setBackground(c);
    }
} 

/*
1  panel.add(yellow)がきいて、OK(core Java 449)。
2  setBackground(c);とすると、色が変わるのは一瞬。
3  contentPane.setBackground(c)もだめ。
 */