Terminate running threads on JFrame close

Question

How do I invoke extra operations when the user closes a JFrame window? I have to stop existing threads.

As I understand it, setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); causes the frame to be closed and its thread to be stopped. Should threads be closed after JFrame.EXIT_ON_CLOSE?

Client:

static boolean TERMINATE = false;
public static void main(String[] args) {
// some threads created
 while(true) {

                if(TERMINATE){
                         // do before frame closed
                    break;
                         }
              }

}
    private static JPanel startGUI(){
            JFrame f = new JFrame();
            f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            JPanel gui = new JPanel();
             f.add( gui);
             f.setSize(500,500);
             f.setVisible(true);
             return gui;
        }

---

I need to close sockets the thread's working with. What is the best practice to do that?

Answer 1

Using JFrame.EXIT_ON_CLOSE actually terminates the JVM (System.exit). All running threads will automatically be stopped.

If you want to perform some action when a JFrame is about to close, use a WindowListener.

JFrame frame = ...
frame.addWindowListener(new WindowAdapter() {
    @Override
    public void windowClosing(WindowEvent e) {
        // close sockets, etc
    }
});

Answer 2

• You have to add a WindowListener to the JFrame.

• Inside the windowClosing method, you can provide required code.

For example:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class ClosingFrame extends JFrame {

    private JMenuBar MenuBar = new JMenuBar();
    private JFrame frame = new JFrame();
    private static final long serialVersionUID = 1L;
    private JMenu File = new JMenu("File");
    private JMenuItem Exit = new JMenuItem("Exit");

    public ClosingFrame() {
        File.add(Exit);
        MenuBar.add(File);
        Exit.addActionListener(new ExitListener());
        WindowListener exitListener = new WindowAdapter() {

            @Override
            public void windowClosing(WindowEvent e) {
                int confirm = JOptionPane.showOptionDialog(frame,
                        "Are You Sure to Close this Application?",
                        "Exit Confirmation", JOptionPane.YES_NO_OPTION,
                        JOptionPane.QUESTION_MESSAGE, null, null, null);
                if (confirm == 0) {
                    System.exit(1);
                }
            }
        };
        frame.addWindowListener(exitListener);
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setJMenuBar(MenuBar);
        frame.setPreferredSize(new Dimension(400, 300));
        frame.setLocation(100, 100);
        frame.pack();
        frame.setVisible(true);
    }

    private class ExitListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent e) {
            int confirm = JOptionPane.showOptionDialog(frame,
                    "Are You Sure to Close this Application?",
                    "Exit Confirmation", JOptionPane.YES_NO_OPTION,
                    JOptionPane.QUESTION_MESSAGE, null, null, null);
            if (confirm == 0) {
                System.exit(1);
            }
        }
    }

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

            @Override
            public void run() {
                ClosingFrame cf = new ClosingFrame();
            }
        });
    }
}

Answer 3

You can set the default close operation on the JFrame

JFrame frame = new JFrame("My Frame");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);