Question

I’m creating an application with Swing, and I’ve got a problem. I want to handle the focusLost() and focusGained() events, but I think my code is buggy.

I’ve got the following, test code:

addWindowFocusListener(new WindowFocusListener() {
    @Override
    public void windowLostFocus(WindowEvent e) {
        System.out.println("Lost!");
        System.out.println(e.toString());
    }

    @Override
    public void windowGainedFocus(WindowEvent e) {
        System.out.println("Gained!");
        System.out.println(e.toString());
    }
});

And, when I activate the window, it seems that app handles 2 events at once:

Gained!
java.awt.event.WindowEvent[WINDOW_GAINED_FOCUS,opposite=null,oldState=0,newState=0] on frame0
Lost!
java.awt.event.WindowEvent[WINDOW_LOST_FOCUS,opposite=null,oldState=0,newState=0] on frame0

And, when I deactivate the window, the program prints nothing.

There’s also more interesting thing. When I open a new JFrame that belongs to my app, the event system works properly, even when I close this second Window.

I just don’t know why it is happening. Please help.

System specs:

• OS: Ubuntu 12.04 x86_64
• JVM: OpenJDK 7

m4tx@m4tx-EP35-DS4:~$ java -version
Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=lcd
java version "1.7.0_03"
OpenJDK Runtime Environment (IcedTea7 2.1.1pre) (7~u3-2.1.1~pre1-1ubuntu3)
OpenJDK 64-Bit Server VM (build 22.0-b10, mixed mode)

Answer 1

Well, I can’t see much wrong with your code; so I put together a quick demo, and it seems to be working fine:

import java.awt.event.WindowEvent;
import java.awt.event.WindowFocusListener;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class WindowEventDemo extends JFrame implements WindowFocusListener {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new WindowEventDemo("Window Event Demo").setVisible(true);
            }
        });
    }

    public WindowEventDemo(String name) {
        super(name);
        addWindowFocusListener(this);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 300);
    }

    @Override
    public void windowGainedFocus(WindowEvent e) {
        System.out.println("WindowFocusListener method called: windowGainedFocus.");
    }

    @Override
    public void windowLostFocus(WindowEvent e) {
        System.out.println("WindowFocusListener method called: windowLostFocus.");
    }
}

On start up it prints:

WindowFocusListener method called: windowGainedFocus.

and when the window is minimized, or the mouse is clicked somewhere else on screen besides the JFrame is prints:

WindowFocusListener method called: windowLostFocus.