How to I terminate a swing GUI programmatically?

Question

Trying to terminate a swing gui, start the same gui and terminate it.

I am using the answer to this question but it seem to only work once.

The code below cycles once and hangs after printing 2.

import java.awt.Toolkit;
import java.awt.event.WindowEvent;
import java.lang.reflect.InvocationTargetException;
import javax.swing.*;
public class Hello {
    void createAndShowGUI() {
        frame=new JFrame("HelloWorldSwing");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JLabel label=new JLabel("Hello World");
        frame.getContentPane().add(label);
        frame.pack();
        frame.setVisible(true);
    }
    void goodbye() {
        WindowEvent wev=new WindowEvent(frame,WindowEvent.WINDOW_CLOSING);
        Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(wev);
    }
    static void helloGoodbye() throws InterruptedException,InvocationTargetException {
        System.out.println("enter");
        final Hello hello=new Hello();
        System.out.println("1");
        javax.swing.SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
                System.out.println("3");
                hello.createAndShowGUI();
                System.out.println("4");
            }
            {
                System.out.println("2");
            }
        });
        System.out.println("5");
        SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
                hello.goodbye();
                System.out.println("6");
            }
        });
        // Thread.sleep(1000);
        System.out.println("exit");
    }
    public static void main(String[] args) throws InvocationTargetException,InterruptedException {
        for(int i=0;i<10;i++)
            helloGoodbye();
        System.out.println("exiting main");
    }
    JFrame frame;
}

Why doesn't it work?

Answer 1

The program doesn't hang but rather it exits because:

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

From the doc:

EXIT_ON_CLOSE (defined in JFrame): Exit the application using the System exit method. Use this only in applications.

Here, it seems like DISPOSE_ON_CLOSE will result in the behavior you are expecting. I also do not really see a reason to be posting this window closing event when you can call setVisible(false) and dispose. Without making assumptions about what the program is actually intended to do, both of these options will result in all 10 frames being shown/hidden/disposed.

I would guess that the reason the program halts after printing the '2' is that calling invokeAndWait causes any previously queued events to be pumped, including the window closing event.