I can use getActionCommand to change the label content, but I can't use it to change the color?

问题

So with the help of others here I finally managed to code a button that alternates the label "Hello World!" to "Hello Universe!" and back again. I used the code below, and used the same way to try and change the color, but it didn't work as expected. I've been searching for hours on this, but with no avail. Thank you for reading, anything helps!

Code:

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

public class Javagame extends JPanel implements ActionListener{
    protected JButton changetext;
    protected JButton red;
    protected JButton green;
    private JLabel label;

    public Javagame() {
        add(changetext = new JButton("Button!"));
        changetext.setPreferredSize(new Dimension(50, 50));
        changetext.setActionCommand("change");

        add(red = new JButton("Red"));
        red.setPreferredSize(new Dimension(50, 50));
        red.setActionCommand("changecolorRed");

        add(green = new JButton("Green"));
        green.setPreferredSize(new Dimension(50, 50));
        green.setActionCommand("changecolorGreen");

        changetext.addActionListener(this);

        label = new JLabel("Hello World!", SwingConstants.CENTER);
        label.setFont(new Font("Arial", Font.BOLD, 20));
        label.setForeground(new Color(0x009900));
        setLayout(new BorderLayout());
        add(label, BorderLayout.CENTER);
        add(changetext, BorderLayout.NORTH);
        add(red, BorderLayout.WEST);
        add(green, BorderLayout.EAST);
    }
    public void actionPerformed(ActionEvent e) {
        if ("change".equals(e.getActionCommand())) {
            label.setText("Hello Universe!");   
            changetext.setActionCommand("changeBack");
        }
        if ("changeBack".equals(e.getActionCommand())) {
            label.setText("Hello World!");
            changetext.setActionCommand("change");
        }
        if ("changecolorRed".equals(e.getActionCommand())) {
            label.setForeground(new Color(0xFF0000));
        }
        if ("changecolorGreen".equals(e.getActionCommand())) {
            label.setForeground(new Color(0x009900));
        }
    }
    private static void createWindow(){
        JFrame frame = new JFrame("Javagame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(500,500));

        JPanel panel = new JPanel(new BorderLayout());

        Javagame newContentPane = new Javagame();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);

        frame.setLocationRelativeTo(null);
        frame.pack();
        frame.setVisible(true);
    }
    public static void main(String[] args) {
        createWindow();
    }
}

回答1:

You need to add ActionListeners to buttons for them to work.

This is usually done via a simple method call: red.addActionListener(someListener);

Also:

• get rid of your setPreferredsize(...) method calls, and instead let components set their own size. At the most you can override getPreferredSize() if need be, but try to limit that.
• Avoid having your GUI code implement your listener interfaces as that leads to confusing and difficult to manage code. Better to use anonymous inner listeners or private inner classes or stand alone listener classes.

---

For example:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class JavaGame2 extends JPanel {
   private static final int PREF_W = 600;
   private static final int PREF_H = 400;
   private static final Font LABEL_FONT = new Font("Arial", Font.BOLD, 20);
   private static final Color[] FOREGROUNDS = { new Color(0x009900),
         new Color(0x990000), new Color(0x000099), new Color(0x999900),
         new Color(0x990099), new Color(0x009999) };
   private static final String[] LABEL_TEXTS = { "Hello World!",
         "Goodbye World!", "Hola Todo el Mundo!", "Hasta la Vista Baby!",
         "Whatever!!" };

   private JButton changetextButton;
   private JButton changeColorButton;
   private JLabel label;
   private int labelTextIndex = 0;
   private int foregroundIndex = 0;

   public JavaGame2() {
      label = new JLabel(LABEL_TEXTS[labelTextIndex], SwingConstants.CENTER);
      label.setFont(LABEL_FONT);
      label.setForeground(FOREGROUNDS[foregroundIndex]);

      // example of anonymous inner ActionListener:
      changetextButton = new JButton("Change Text");
      changetextButton.addActionListener(new ActionListener() {

         @Override
         public void actionPerformed(ActionEvent evt) {
            labelTextIndex++;
            labelTextIndex %= LABEL_TEXTS.length;
            label.setText(LABEL_TEXTS[labelTextIndex]);
         }
      });

      // example of use of an anonymous AbstractAction:
      changeColorButton = new JButton(new AbstractAction("Change Color") {

         @Override
         public void actionPerformed(ActionEvent e) {
            foregroundIndex++;
            foregroundIndex %= FOREGROUNDS.length;
            label.setForeground(FOREGROUNDS[foregroundIndex]);
         }
      });

      setLayout(new BorderLayout());
      add(changetextButton, BorderLayout.NORTH);
      add(changeColorButton, BorderLayout.SOUTH);
      add(label, BorderLayout.CENTER);
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private static void createAndShowGui() {
      JavaGame2 mainPanel = new JavaGame2();

      JFrame frame = new JFrame("Java Game 2");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

来源：https://stackoverflow.com/questions/16875731/i-can-use-getactioncommand-to-change-the-label-content-but-i-cant-use-it-to-ch