在Java中显示来自按钮的不同图像

Question

我正在编写一个程序，用户可以从中选择3个不同的按钮，根据他们选择的按钮，会出现不同的图像（或者在这种情况下为gif）。我将程序拆分为3个类：GUI Window类，GUI类和Color Panel类。问题是单击按钮时无法加载图像。

/******************************GUIWindow*******************************/
import javax.swing.*;

public class GUIWindow
{
    public static void main(String[] args)
    {
        GUI theGUI = new GUI();
        theGUI.setTitle("Merry Christmas!");
        theGUI.setSize(500, 600);
        theGUI.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        theGUI.setVisible(true);
    }
}

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

public class GUI extends JFrame
{
    private ImageIcon cat1 = new ImageIcon("cat1.gif");
    private ImageIcon cat2 = new ImageIcon("cat2.gif");
    private JButton cat1Button = new JButton("1");
    private JButton cat2Button = new JButton("2");
    private JButton cat3Button = new JButton("3");

    public GUI()
    {
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(cat1Button);
        buttonPanel.add(cat2Button);
        buttonPanel.add(cat3Button);

        Container container = getContentPane();
        container.add(buttonPanel, BorderLayout.NORTH);

        cat1Button.addActionListener(new cat1Listener());
        cat2Button.addActionListener(new cat2Listener());
    }

    private class cat1Listener implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            ColorPanel panel = new ColorPanel(Color.white, cat1);
            Container pane = getContentPane();
            pane.add(panel);
        }
    }

    private class cat2Listener implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            ColorPanel panel = new ColorPanel(Color.white, cat2);
            Container pane = getContentPane();
            pane.add(panel);
        }
    }
}

/******************************ColorPanel*******************************/
import java.awt.*;
import javax.swing.*;

public class ColorPanel extends JPanel
{
    private ImageIcon image;

       public ColorPanel(Color backColor, ImageIcon i)
       {
          setBackground(backColor);
          image = i;
        }

       public void paintComponent(Graphics g)
       {
          super.paintComponent(g);

          int x = (getWidth() - image.getIconWidth()) / 2;
          int y = (getHeight() - image.getIconHeight()) / 2;

          image.paintIcon(this, g, x, y);
       }
}