Java：MouseListener，KeyListener和PaintComponent的JFrame问题

Question

I have an issue in which my mouseListener is unresponsive. I have tried to add a mouseListener to one object, a keyListener to another, and a paintComponent to another and then put all the objects onto the JFrame. My problem is that the mouseListener isn't responding but the keyListener and the paintComponent are. Here is my code:

public JFrame frame = new JFrame("JFrame Test");

public static void main(String[]args) {
    new JFrameTest();
}

public JFrameTest() {
    frame.setSize(100, 100);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setResizable(false);
    frame.add(new keys());
    frame.add(new mouse());
    frame.add(new render());
    frame.setVisible(true);
}

@SuppressWarnings("serial")
public class render extends JPanel {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.fillRect(0, 0, frame.getWidth() / 2, frame.getHeight() / 2);
        repaint();
    }
}

@SuppressWarnings("serial")
public class keys extends JPanel {
    public keys() {
        setFocusable(true);
        addKeyListener(new KeyAdapter() {
            public void keyPressed(KeyEvent e) {
                System.out.println("Key Pressed!");
            }

            public void keyReleased(KeyEvent e) {
                System.out.println("Key Released!");
            }
        });
    }
}

@SuppressWarnings("serial")
public class mouse extends JPanel {
    public mouse() {
        setFocusable(true);
        addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                System.out.println("Mouse Pressed!");
            }

            public void mouseReleased(MouseEvent e) {
                System.out.println("Mouse Released!");
            }
        });
    }
}

I made sure the mouseListener and the keyListener are both setFocusable(true) and the paintComponent was added last so it actually displays. It appears as though if I switch the order of adding the keyListener object and the mouseListener object then neither works. If you have any ideas on how to fix it I would be grateful. Thanks!

Answer 1

I'll tell you what the problem is, the JFrame uses BroderLayout as its default layout manager. So when you do frame.add() three times in a row without specifying the location of where the JPanel is being added you are over-writing the same panel 3 times in a row.

So the last thing you add will be there.

Try this...

frame.add(new keys(), BorderLayout.NORTH);
frame.add(new mouse(), BorderLayout.SOUTH);
frame.add(new render(), BorderLayout.CENTER);

Just as a side note, this looks like a really weird way to program. You are better off creating 1 class that extends JPanel and adding a key listener and mouse listener to it. And override its paintComponent() method to do your rendering.