Question

This is my code :

public class JJD extends JFrame {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public JJD() {
        super("test");

        JPanel center = new JPanel();
        center.setBackground(Color.red);
        JScrollPane pane = new JScrollPane(center);

        this.getContentPane().add(pane, BorderLayout.CENTER);
        final JFrame fr = this;
        this.addWindowFocusListener(new WindowFocusListener() {

            @Override
            public void windowLostFocus(WindowEvent arg0) {
                // TODO Auto-generated method stub

                if (fr.isValid()) {
                    System.out.println("FOCUS VALID!");
                } else {
                    System.out.println("Focus INVALID");
                }
            }

            @Override
            public void windowGainedFocus(WindowEvent arg0) {
                // TODO Auto-generated method stub

            }
        });

        this.setVisible(true);
        this.setSize(500, 500);
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        JFrame fr = new JJD();
        fr.validate();

    }

}

Could you tell my why the listener prints out that my frame is not valid? I tried also other methods like pack() revalidate() and still, the listener prints out that my frame is not valid.

HINT : The problem is because of the JScrollPane but I can’t figure out how to make my frame valid.

Answer 1

I think it might be because you are not override windowsGainedFocus method .

public void windowGainedFocus(WindowEvent arg0) {
    if (fr.isValid()) {
        System.out.println("FOCUS VALID!");
    } else {
        System.out.println("Focus INVALID");
    }
}

You can override it just like the other one and look if it is valid. If it is not work you can add fr.validate() method call inside the else clause. I hope it would help.