JLabel ToolTip interferes with MouseListener

Question

I have Java Swing application ToolTipMouseTest

The critical line is label.setToolTipText("label" + i);. Once it is commented out very click on a label produces 2 mousePressed in console. With this line enabled click on labels would produce nothing.

Is this expected behaviour or a bug? My goal is to show tooltips without disabling MouseListener from working.

Almost SSCCE, but without imports:

public class ToolTipMouseTest {

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new ToolTipMouseTest();
        }
    });
}

public ToolTipMouseTest() {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLayout(new BorderLayout());

    JLayeredPane lpane = new JLayeredPane() {
        @Override
        public Dimension getPreferredSize() {
            return new Dimension(600,400);
        }
    };

    MouseAdapter1 mouseAdapter1 = new MouseAdapter1();
    lpane.addMouseListener(mouseAdapter1);

    frame.add(lpane);

    JPanel panel1 = new JPanel();
    panel1.setSize(new Dimension(600, 400));
    panel1.setOpaque(false);

    lpane.add(panel1, JLayeredPane.PALETTE_LAYER);

    JPanel panel2 = new JPanel();
    for (int i = 0; i < 5; i++) {
        JLabel label = new JLabel("Label " + i);
        panel2.add(label);
        label.setToolTipText("label" + i); //HERE!!
    }

    JScrollPane spane = new JScrollPane(panel2) {
        private static final long serialVersionUID = 1L;

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(300, 200);
        }
    };

    MouseAdapter2 mouseAdapter2 = new MouseAdapter2();
    spane.addMouseListener(mouseAdapter2);

    panel1.add(spane);

    frame.pack();
    frame.setVisible(true);
}

private class MouseAdapter1 extends MouseAdapter {
    @Override
    public void mousePressed (MouseEvent me) {
        System.out.println("1 mousePressed");
    }
}

private class MouseAdapter2 extends MouseAdapter {
    @Override
    public void mousePressed (MouseEvent me) {
        System.out.println("2 mousePressed");
    }
}
}

Answer 1

It is working as intended. Let me explain why.

When you are adding a tooltip to any component (labels in your case) they automatically recieve a new mouse listeners from ToolTipManager. Here is the register method from ToolTipManager class:

public void registerComponent(JComponent component) {
    component.removeMouseListener(this);
    component.addMouseListener(this);
    component.removeMouseMotionListener(moveBeforeEnterListener);
    component.addMouseMotionListener(moveBeforeEnterListener);
    component.removeKeyListener(accessibilityKeyListener);
    component.addKeyListener(accessibilityKeyListener);
}

When any component has atleast one mouse listener set on it - it will block any mouse enter/exit/click/press/release events (mouse dragged/moved in case there is mouse motion listener set) from going down in the components hierarchy.

In your case - labels blocking mouse events and mouse motion events from going down to layered pane due to ToolTipManager listeners installed when tooltip is set.

This could be avoided if you make a workaround listener with that will pass events down. For example you can add that listener to every component with a tooltip that should pass mouse events down.

Here is a small example of how that could be done:

label.addMouseListener ( new MouseAdapter ()
{
    public void mousePressed ( MouseEvent e )
    {
        lpane.dispatchEvent ( SwingUtilities.convertMouseEvent ( e.getComponent (), e, lpane ) );
    }
} );

In that case event will be passed to layered pane though. Anyway you can dispatch this even anywhere you want (i guess it would be spane in your case).