除了与mouselistener一起使用外，JLabel不会显示

Question

I'm working on java game and when i add JPanel with JLabel buttons to JFrame, buttons don't show up until i hover over them. I tried removing mouselistener, but it just makes buttons invisible even if i hover over them. I also tried: validate(),revalidate(), changing order of adding components to Jframe.

Game.java:

    import javax.swing.*;
    public class Game {
    public static void main(String[] args) {
        JFrame ramka = new JFrame();
        ramka.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        ramka.setTitle("Super Boxxy");
        ramka.setResizable(false);
        ramka.pack();
        ramka.setLocationRelativeTo(null);
        Menu window = new Menu(ramka);
        window.ZbudujMenu(ramka);
     }
    }

Menu.java:

    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.MouseEvent;
    import java.awt.event.MouseListener;
    import static java.lang.Thread.sleep;

public class Menu extends JLabel implements MouseListener {
public Menu(JFrame ramka){
   this.ramka=ramka;
}
//Title Screen
JFrame ramka;
JLabel startButton;
JLabel exitButton;
ImageIcon titleIcon;
JLabel backgroundImg;
JPanel menu;

public static final int WIDTH = 1024;
public static final int HEIGHT = 640;

ImageIcon exitIcon =new ImageIcon("resources/exit.png");
ImageIcon exitIconHover =new ImageIcon("resources/exit_hover.png");

ImageIcon startIcon =new ImageIcon("resources/start.png");
ImageIcon startIconHover =new ImageIcon("resources/start_hover.png");

public void ZbudujMenu(JFrame ramka) {
    //Start button
    startButton = new JLabel();
    startButton.setIcon(startIcon);
    startButton.addMouseListener(this);


    //Exit button
    exitButton=new JLabel();
    exitButton.setIcon(exitIcon);
    exitButton.addMouseListener(this);


    //Background
    titleIcon =new ImageIcon("resources/background.png");
    backgroundImg = new JLabel(titleIcon);
    backgroundImg.setBounds(0,0,WIDTH,HEIGHT);
    backgroundImg.setLayout(new FlowLayout());


    //Frame
    ramka.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ramka.setSize (WIDTH,HEIGHT);
    ramka.setTitle("Super Boxxy");

    menu = new JPanel(new GridLayout(2, 1, 8, 8));
    menu.add(startButton);
    menu.add(exitButton);
    menu.setBorder(BorderFactory.createEmptyBorder(353,370,54,370));

    ramka.add(backgroundImg);
    ramka.add(menu);
    ramka.setVisible(true);
    ramka.setLocationRelativeTo(null);


}
public void mouseClicked(MouseEvent akcja)
{
}
public void mouseEntered(MouseEvent akcja)
{
    if (akcja.getSource() == startButton)
    {
       startButton.setIcon(startIconHover);
    }
    else if (akcja.getSource() == exitButton)
    {
        exitButton.setIcon(exitIconHover);
    }
}
    public void mouseExited(MouseEvent akcja)
    {
       if (akcja.getSource() == startButton)
        {
            startButton.setIcon(startIcon);
        }
        else if (akcja.getSource() == exitButton)
        {
            exitButton.setIcon(exitIcon);
        }
    }
    public void mousePressed(MouseEvent akcja) {}
    public void mouseReleased(MouseEvent akcja) {}
}

Answer 1

Component should be added to the frame before the frame is made visible.

JFrame ramka = new JFrame();
ramka.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
ramka.setTitle("Super Boxxy");
ramka.setResizable(false);
ramka.pack();

You create a frame and pack it without adding any components to the frame. You invoke the pack() method AFTER adding components to the frame so all the components can be displayed at their preferred size.

public class Menu extends JLabel implements MouseListener {  

Why are you extending JLabel? You are not adding any new functionality to the label.

I would suggest your class should:

1. Extend JPanel so you can add all your components to the panel
2. all the code in the ZbudujMenu(...) method would be moved to the constructor of the Menu() class.
3. get rid of all the JFrame logic from the Menu class.

Then the code in main() method would look something like:

    JFrame ramka = new JFrame();
    ramka.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ramka.setTitle("Super Boxxy");
    ramka.add( new Menu() ):
    ramka.setResizable(false);
    ramka.pack();
    ramka.setLocationRelativeTo(null);
    ramka.setVisible( true );
    //Menu window = new Menu(ramka);
    //window.ZbudujMenu(ramka);

Read the Swing tutorial . There a plenty of demo programs that will show you how to create a GUI using this basic structure. The demos will also show you how to create your GUI on the Event Dispatch Thread (EDT) . All Swing components should be created on the EDT .