java – 面板中的背景颜色不会改变

下面的代码生成一个带按钮的窗口,但是当我运行i并按下按钮时会弹出一条错误消息.根据Spring工具提示：

Cannot make a static reference to the non-static method setBackground(Color) from the type JComponent

据我所知,这个程序实际上是从我的Java教科书行输入的.这是一本较旧的书,因此可能存在不兼容性,但似乎不太可能.

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

public class ButtonTest
{
    public static void main(String[] args)
    {
        final ButtonFrame frame = new ButtonFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.show();
}
}

class ButtonFrame extends JFrame
{
    public ButtonFrame()
    {
    setTitle("Button Test");
    setSize(Default_width, Default_height);

        //panel
        ButtonPanel panel = new ButtonPanel();
        Container contentPane=getContentPane();
        contentPane.add(panel);
    }

    public static final int Default_width = 300;
public static final int Default_height = 200;
}

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

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

    ColorAction yellowAction= new ColorAction(Color.YELLOW);
    ColorAction redAction = new ColorAction(Color.RED);
    ColorAction blueAction = new ColorAction(Color.BLUE);

    yellowButton.addActionListener(yellowAction);
    blueButton.addActionListener(blueAction);
    redButton.addActionListener(redAction);
    }
}

    class ColorAction implements ActionListener
    {
        public ColorAction(Color c)
    {
        backgroundColor=c;
    }

    public void actionPerformed(ActionEvent event)
    {
    ButtonPanel.setBackground(backgroundColor);
    }

        private Color backgroundColor;
}

解决方法:

一种方法是将nest ColorAction作为ButtonPanel中的内部类,它可以隐式访问封闭面板.

附录：如@Andrew Thompson和@nachokk的评论中所述,隐式可访问性可以通过使用封闭类名限定来明确.有关详情,请参阅JLS §15.8.4. Qualified this.在此示例中,这两个调用是等效的：

 setBackground(backgroundColor);
 ButtonPanel.this.setBackground(backgroundColor);

作为更通用的替代方案,请考虑在Action中封装目标面板和颜色,如here所述.

class ButtonPanel extends JPanel {

    public ButtonPanel() {
        JButton yellowButton = new JButton("Yellow");
        JButton blueButton = new JButton("Blue");
        JButton redButton = new JButton("Red");

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

        ColorAction yellowAction = new ColorAction(Color.YELLOW);
        ColorAction redAction = new ColorAction(Color.RED);
        ColorAction blueAction = new ColorAction(Color.BLUE);

        yellowButton.addActionListener(yellowAction);
        blueButton.addActionListener(blueAction);
        redButton.addActionListener(redAction);
    }

    private class ColorAction implements ActionListener {

        public ColorAction(Color c) {
            backgroundColor = c;
        }

         @Override
         public void actionPerformed(ActionEvent event) {
            setBackground(backgroundColor);
        }
        private Color backgroundColor;
    }
}

标签：setbackground,java,swing,jpanel
来源： https://codeday.me/bug/20190825/1719157.html