Checkboxes not showing up

问题:

I am hoping another set of eyes can help me find where my code is wrong. I can compile and run the program, but all I get is a white screen. It's supposed to show the checkboxes and change the background to whichever color is chosen. Any help is appreciated!

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

public class Chapter5Debug extends Frame implements ItemListener
{
static Chapter5Debug f = new Chapter5Debug();

CheckboxGroup options = new CheckboxGroup();
    Checkbox blue = new Checkbox("Blue",false,options);
    Checkbox red = new Checkbox("Red",false,options);
    Checkbox yellow = new Checkbox("Yellow",false,options);
    Checkbox pink = new Checkbox("Pink",false,options);
    Checkbox gray = new Checkbox("Gray",false,options);


public void Chapter5Debug()
{
    this.setLayout(new FlowLayout());
    add(blue);
    add(red);
    add(yellow);
    add(pink);
    add(gray);
    blue.addItemListener(this);
    red.addItemListener(this);
    yellow.addItemListener(this);
    pink.addItemListener(this);
    gray.addItemListener(this);

    //overriding windowClosing() allows user to click Close button
    addWindowListener(
        new WindowAdapter()
        {
           public void windowClosing(WindowEvent e)
           {
                System.exit(0);
           }
        }
    );

} //end of constructor method

public static void main(String[] args)
{
    //ColorButtons f = new ColorButtons();
    f.setBounds(200,200,500,100);
    f.setTitle("What's My Color?");
    f.setVisible(true);
} //end of main

public void actionPerformed(ActionEvent e)
{
    if (blue.getState()) f.setBackground(Color.blue);
    else if (red.getState()) f.setBackground(Color.red);
    else if (yellow.getState()) f.setBackground(Color.yellow);
    else if (pink.getState()) f.setBackground(Color.pink);
    else if (gray.getState()) f.setBackground(Color.gray);
} //end of actionPerformed method

public void itemStateChanged(ItemEvent e)
{
}

} //end of class

回答1:

This is not a constructor:

public void Chapter5Debug()
{

it's a void method. You want a constructor? Remove the void keyword.

---

In this line

static Chapter5Debug f = new Chapter5Debug();

you are calling the default constructor, the void method you have is never called.

回答2:

There is code in actionPerformed, but the class is not an actionListener.

Move that code to itemStateChanged that executes when a checkbox is selected. You may need to add f.repaint() after changing the background color to show the change.