How to close a Java Swing application from the cod

Question

What is the proper way to terminate a Swing application from the code, and what are the pitfalls?

I'd tried to close my application automatically after a timer fires. But just calling dispose() on the JFrame didn't do the trick - the window vanished but the application did not terminate. However when closing the window with the close button, the application does terminate. What should I do?

Answer 1

Take a look at the Oracle Documentation.

Starting from JDK 1.4 an Application terminates if:

• There are no displayable AWT or Swing components.
• There are no native events in the native event queue.
• There are no AWT events in java EventQueues.

Cornercases:

The document states that some packages create displayable components without releasing them.A program which calls Toolkit.getDefaultToolkit() won't terminate. is among others given as an example.

Also other Processes can keep AWT alive when they, for what ever reason, are sending events into the native event queue.

Also I noticed that on some Systems it takes a coupple of seconds before the Application actually terminates.

Answer 2

May be the safe way is something like:

    private JButton btnExit;
    ...
    btnExit = new JButton("Quit");      
    btnExit.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e){
            Container frame = btnExit.getParent();
            do 
                frame = frame.getParent(); 
            while (!(frame instanceof JFrame));                                      
            ((JFrame) frame).dispose();
        }
    });

Answer 3

Try:

System.exit(0);

Crude, but effective.

Answer 4

I think, the idea is here the WindowListener - you can add any code there that you'd like to run before the thing shuts down

Answer 5

If I understand you correctly you want to close the application even if the user did not click on the close button. You will need to register WindowEvents maybe with addWindowListener() or enableEvents() whichever suits your needs better.

You can then invoke the event with a call to processWindowEvent(). Here is a sample code that will create a JFrame, wait 5 seconds and close the JFrame without user interaction.

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

public class ClosingFrame extends JFrame implements WindowListener{

public ClosingFrame(){
    super("A Frame");
    setSize(400, 400);
            //in case the user closes the window
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            setVisible(true);
            //enables Window Events on this Component
            this.addWindowListener(this);

            //start a timer
    Thread t = new Timer();
            t.start();
    }

public void windowOpened(WindowEvent e){}
public void windowClosing(WindowEvent e){}

    //the event that we are interested in
public void windowClosed(WindowEvent e){
    System.exit(0);
}

public void windowIconified(WindowEvent e){}
public void windowDeiconified(WindowEvent e){}
public void windowActivated(WindowEvent e){}
public void windowDeactivated(WindowEvent e){}

    //a simple timer 
    class Timer extends Thread{
           int time = 10;
           public void run(){
     while(time-- > 0){
       System.out.println("Still Waiting:" + time);
               try{
                 sleep(500);                     
               }catch(InterruptedException e){}
             }
             System.out.println("About to close");
    //close the frame
            ClosingFrame.this.processWindowEvent(
                 new WindowEvent(
                       ClosingFrame.this, WindowEvent.WINDOW_CLOSED));
           }
    }

    //instantiate the Frame
public static void main(String args[]){
          new ClosingFrame();
    }

}

As you can see, the processWindowEvent() method causes the WindowClosed event to be fired where you have an oportunity to do some clean up code if you require before closing the application.

Answer 6

In response to other comments, DISPOSE_ON_CLOSE does not seem to properly exit the application - it only destroys the window, but the application will continue running. If you want to terminate the application use EXIT_ON_CLOSE.