从扩展的 JPanel Class 看不到 ImageIcon

Question

I have a Class that extends a JPanel and I want it to display an ImageIcon. Something does not seem to work through. map.png is found and when I print out its size in the class is's correct. Also, I made the panel black so I know that the panel works but not the ImageIcon.

However when I place the same code from TestPanel.java into the constructor of GUI.java the ImageIcon works.

Can someone tell me why the ImageIcon does not work in TestPanel.java but it does in GUI.java?

Here is my code

TestPanel.java

public class TestPanel extends JPanel {
    
    public static JLabel map = new JLabel();

    public TestPanel() {
        this.setLayout(null); //to prevent icon from taking the whole screen
        this.setVisible(true); //make frame visible
        this.setBounds(0, 0, 100, 100);
        
        this.setBackground(new Color(0,0,0));
        
        Image imageToScale = new ImageIcon("map.png").getImage();
        double scale = .9; //scale
        int x = (int) (imageToScale.getWidth(null) * scale); //leave image observer as null because we know that the image is loaded
        int y = (int) (imageToScale.getHeight(null) * scale);
        Image scaledImage = imageToScale.getScaledInstance( x, y, java.awt.Image.SCALE_SMOOTH); //scale the image
        ImageIcon image = new ImageIcon(scaledImage); //case the image into an image icon
        
        this.setBounds(0, -4, image.getIconWidth(), image.getIconHeight()); //set position and size of panel to the size of the image. -4 on the Y position because it was not aligned with the top
     
        map.setIcon(image); //set icon for map label
        this.add(map); //add label to panel
    }
}

GUI.java

public class GUI extends JFrame {
    
    public static JPanel problemPanel = new JPanel(); //panel where the points and path will be displayed
    public static JLabel map = new JLabel();
    
    public static TestPanel test = new TestPanel();
    
    public GUI() {
        this.setLayout(null); //to prevent icon from taking the whole screen
        
        this.add(test);
        
        //Frame
        this.setVisible(true); //make frame visible
        this.setSize(1200,1000); //set frame size
        this.setTitle("Travelling Apache Pizza Delivery Driver Problem (TAPDDP)"); //set title of panel
        this.setDefaultCloseOperation(this.EXIT_ON_CLOSE); //terminates program when frame is closed
        this.setLocationRelativeTo(null); //open frame in the middle of the screen
        this.setResizable(false); //prevent resizing of GUI
        

    }

}

Answer 1

I fixed the code by removing this.setLayout(null);in the TestPanel class.