Scope problems with 'this' keyword

Question

I am trying to create my own window class which extends JFrame. However, I am having a problem with the action listener for fullScreenBtn. When writing the ActionListener.actionPerformed funcion, I am unable to use the this keyword as it refers to new ActionListener. How do I refer to the instance of MyWindow instead?

public class MyWindow extends JFrame {
    private static GraphicsEnvironment gEnv = GraphicsEnvironment.getLocalGraphicsEnvironment();
    private static GraphicsDevice gDev = gEnv.getDefaultScreenDevice();
    private static JPanel toolbar = new JPanel();
    private static JButton fullScreenBtn = new JButton("Show Full Screen");
    private static boolean isFullScreen = false;

    public MyWindow() {
        toolbar.setLayout(new FlowLayout());
        this.getContentPane().add(toolbar, BorderLayout.PAGE_START);

        fullScreenBtn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                // Toggle full screen window
                this.setUndecorated(!isFullScreen);
                this.setResizable(isFullScreen);
                gDev.setFullScreenWindow(this);

                isFullScreen = !isFullScreen;

                if (isFullScreen) {
                    fullScreenBtn.setText("Show Windowed");
                } else {
                    fullScreenBtn.setText("Show Full Screen");
                }
            }
        });

        this.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent windowEvent) {
                this.dispose();
                System.exit(0);
            }
        });
    }
}

Hovercraft Full Of Eels · Accepted Answer · 2013-03-23T14:53:31.153

In inner classes you will need to prepend your use of this with the class name of the outer class if you need to obtain a reference to the outer class: For example, use

MyWindow.this.setUndecorated(...)` 
//  etc...

As an aside, you really don't want to extend JFrame here, and in most situations.

Also, the ancestor Window that holds the JButton can be obtained in other ways such as via SwingUtilities.getWindowAncestor(theButton). i.e.,

        public void actionPerformed(ActionEvent e) {
            Object source = e.getSource();
            if (source instanceof JButton) {
              JButton button = (button) source;
              Window ancestorWin = SwingUtilities.getAncestorWindow(button);
              ancestorWin.setUndecorated(!isFullScreen);
              ancestorWin.setResizable(isFullScreen);
              // etc...

Or if you know most definitely that the ancestor window is a JFrame:

        public void actionPerformed(ActionEvent e) {
            Object source = e.getSource();
            if (source instanceof JButton) {
              JButton button = (button) source;

              JFrame ancestorWin = (JFrame) SwingUtilities.getAncestorWindow(button);
              ancestorWin.setUndecorated(!isFullScreen);
              ancestorWin.setResizable(isFullScreen);
              // etc...

Just vote to close this question, which is an obvious duplicate. — Matt Ball, Mar 23 '13 at 14:49
Thanks for the quick reply! I knew there had to be a simple way of doing it. How would you recommend creating this kind of class without extending JFrame? — MTCoster, Mar 23 '13 at 14:51
@MattBall: yes, you are right. If you find the dup, I will add my vote. Edit: vote added. — Hovercraft Full Of Eels, Mar 23 '13 at 15:00

score 3 · Answer 2 · answered Mar 23 '13 at 14:50

3

This is the syntax of accessing the enclosing-class's instance from an inner-class or an anonymous-class:

OuterClass.this.foo();

answered Mar 23 '13 at 14:50

Eng.Fouad

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score 1 · Answer 3 · answered Mar 23 '13 at 14:50

Because you are using an anonymous class, this will refer to that class, in this case the ActionListener. Because your ActionListener doesn't have methods such as setUndecorated, this will give you a compile error.

What you want to do is use MyWindow.this, followed by any method of MyWindow.

score 1 · Answer 4 · answered Mar 23 '13 at 14:51

1

You will need to access this by specifying the outer class too, in your case it has to be something like follows:

MyWindow.this

answered Mar 23 '13 at 14:51

Amar

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Scope problems with 'this' keyword

4 Answers4