一个关于背景颜色改变的问题

[magicshop]

这是一个改变背景颜色的程序，但运行后颜色没改变阿？
请帮忙看看。谢谢

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

class FirstPanel extends JPanel
implements ActionListener
{ public FirstPanel()
{ JButton redButton = new JButton("Red");
JButton blueButton = new JButton("Blue");
JButton yellowButton = new JButton("Yellow");

add(redButton);
add(blueButton);
add(yellowButton);

redButton.addActionListener(this);
blueButton.addActionListener(this);
yellowButton.addActionListener(this);
}

public void actionPerformed(ActionEvent evt)
{ Object source = evt.getSource();
Color color = getBackground();
if (source == redButton) color = Color.red;
else if (source == blueButton) color = Color.blue;
else if (source == yellowButton) color = Color.yellow;
setBackground(color);
repaint();
}
private JButton redButton;
private JButton blueButton;
private JButton yellowButton;
}
class FirstFrame extends JFrame
{ public FirstFrame()
{ setTitle("FirstFrame");
setSize(300, 200);
addWindowListener(new WindowAdapter()
{ public void windowClosing(WindowEvent e)
{ System.exit(0);
}
});

Container contentPane = getContentPane();
contentPane.add(new FirstPanel());
}
}

public class FirstTest
{ public static void main(String[] args)
{ JFrame frame = new FirstFrame();
frame.setVisible(true);
}
}

[magicshop]

自己推一下吧:((((

[shihb]

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

class FirstPanel extends JPanel
implements ActionListener
{ public FirstPanel()
{ JButton redButton = new JButton("Red");//你在这个地方不应该再定义三个JButton，你把这三个button前的JButton去掉就可以了！你试试！
JButton blueButton = new JButton("Blue");
JButton yellowButton = new JButton("Yellow");

add(redButton);
add(blueButton);
add(yellowButton);

redButton.addActionListener(this);
blueButton.addActionListener(this);
yellowButton.addActionListener(this);
}

public void actionPerformed(ActionEvent evt)
{ Object source = evt.getSource();
Color color = getBackground();
if (source == redButton) color = Color.red;
else if (source == blueButton) color = Color.blue;
else if (source == yellowButton) color = Color.yellow;
setBackground(color);
repaint();
}
private JButton redButton;
private JButton blueButton;
private JButton yellowButton;
}
class FirstFrame extends JFrame
{ public FirstFrame()
{ setTitle("FirstFrame");
setSize(300, 200);
addWindowListener(new WindowAdapter()
{ public void windowClosing(WindowEvent e)
{ System.exit(0);
}
});

Container contentPane = getContentPane();
contentPane.add(new FirstPanel());
}
}

public class FirstTest
{ public static void main(String[] args)
{ JFrame frame = new FirstFrame();
frame.setVisible(true);
}
}

[drinkant]

错误在于
private JButton redButton;
private JButton blueButton;
private JButton yellowButton;
然后构造器中再
JButton redButton = new JButton("Red");
JButton blueButton = new JButton("Blue");
JButton yellowButton = new JButton("Yellow");
明白 ? 一开始偶也被迷惑了. . . . .

[magicshop]

真的阿！
我不明白为什么要有private JButton redButton;这几句话，作用是什么阿？
为什么有了这几句话前面加上JButton就无法改变颜色呢？请赐教！

[shihb]

你在构造函数中又定义了一组button,这是不对的！因为你在构造函数中定义的button只会在你的构造函数中有效，而在你的perform方法中就不知道是什么了！所以你的这组button应该在定义成成员变量，而不是一个方法中的变量！

[drinkant]

cow
被你打败了
很简单,在构造器中你的JButton redButton跟private JButton redButton根本就不是同一个JButton,作用域不同 !
看来你一点基础知识也没有呀. ..

good good study,day day up !

[magicshop]

to 喝酒的蚂蚁
我一点基础知识也没有居然都让你给看出来了，你咋这么聪明呢。我为我还能不能有美好的未来而郁闷

[magicshop]

谢谢你们的帮助