Close program with keypress during a loop

Question

I'd like to stop the program if F10 key was pressed. This code types a 1000 times. I am using jnativehook library (https://github.com/kwhat/jnativehook/wiki/Usage).

The program runs (with F9) but it doesn't stop when I press F10.

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package jnativehook01;

import java.awt.AWTException;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.datatransfer.Clipboard;
import java.awt.datatransfer.StringSelection;
import java.awt.event.KeyEvent;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import org.jnativehook.GlobalScreen;
import org.jnativehook.NativeHookException;
import org.jnativehook.dispatcher.SwingDispatchService;
import org.jnativehook.keyboard.NativeKeyEvent;
import org.jnativehook.keyboard.NativeKeyListener;

public class SwingExample extends JFrame implements NativeKeyListener, WindowListener {
    private static final long serialVersionUID = 1L;

    public SwingExample() {
        // Set the event dispatcher to a swing safe executor service.
        GlobalScreen.setEventDispatcher(new SwingDispatchService());

        setTitle("JNativeHook Swing Example");
        setSize(300, 150);
        setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        addWindowListener(this);
        setVisible(true);
    }

    public void windowOpened(WindowEvent e) {
        // Initialze native hook.
        try {
            GlobalScreen.registerNativeHook();
        }
        catch (NativeHookException ex) {
            System.err.println("There was a problem registering the native hook.");
            System.err.println(ex.getMessage());
            ex.printStackTrace();

            System.exit(1);
        }

        GlobalScreen.addNativeKeyListener(this);
    }


    public void windowClosing(WindowEvent e) { /* Unimplemented */ }
    public void windowIconified(WindowEvent e) { /* Unimplemented */ }
    public void windowDeiconified(WindowEvent e) { /* Unimplemented */ }
    public void windowActivated(WindowEvent e) { /* Unimplemented */ }
    public void windowDeactivated(WindowEvent e) { /* Unimplemented */ }

    // Start program (F9)
    public void nativeKeyReleased(NativeKeyEvent e) {
        if (e.getKeyCode() == NativeKeyEvent.VC_F9) {

            Robot bot;  
            try {
                String text = "a";
                StringSelection stringSelection = new StringSelection(text);
                Clipboard clipboard = Toolkit.getDefaultToolkit().getSystemClipboard();
                clipboard.setContents(stringSelection, stringSelection);

                bot = new Robot();

                for (int i = 0; i < 1001; i++) {

                    //t
                    bot.keyPress(KeyEvent.VK_T);
                    bot.delay(100);
                    bot.keyRelease(KeyEvent.VK_T);

                    bot.delay(500);

                    // Type "a"
                    bot.keyPress(KeyEvent.VK_CONTROL);
                    bot.keyPress(KeyEvent.VK_V);
                    bot.keyRelease(KeyEvent.VK_V);
                    bot.keyRelease(KeyEvent.VK_CONTROL);

                    bot.delay(500);

                    //Enter

                    bot.keyPress(KeyEvent.VK_ENTER);
                    bot.keyRelease(KeyEvent.VK_ENTER);

                    if (e.getKeyCode() == NativeKeyEvent.VC_F10) {
                         System.exit(1);
                    }

                    // Wait 4 sec for the new fill
                    bot.delay(4000);

                }

            } catch (AWTException e1) {
            }
        }


    }

    public void nativeKeyPressed(NativeKeyEvent e) { /* Unimplemented */ }
    public void nativeKeyTyped(NativeKeyEvent e) { /* Unimplemented */ }

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

    @Override
    public void windowClosed(WindowEvent e) {
        // TODO Auto-generated method stub

    }
}

Does it ever come to the If condition `if (e.getKeyCode() == NativeKeyEvent.VC_F10)`? Because I am unsure if it'd ever come inside it! while you have outer If statement with `if (e.getKeyCode() == NativeKeyEvent.VC_F9)`. — Procrastinator, Sep 18 '17 at 13:23
Yes I think you're right. When the for loop arrives the if (e.getKeyCode() == NativeKeyEvent.VC_F10) { line I don't know if this has enough time to check if someone pressed F10 or not. I'd like to be able to terminate the program during every for iteration. — fini, Sep 18 '17 at 17:18
You can probably check it by putting the IF statement outside the IF condition of the key F9. — Procrastinator, Sep 18 '17 at 18:09

score 1 · Accepted Answer · answered Sep 18 '17 at 13:46

More Likely problem seems to be inside the if block

if (e.getKeyCode() == NativeKeyEvent.VC_F10) {
                     System.exit(1);
                }

System.exit(1) is to be used when some error has occured so System.exit(1) is mostly used in Catch block.

if (e.getKeyCode() == NativeKeyEvent.VC_F10) {
                     System.exit(0);return;
                }

This should do the job. For reference System.exitDetail TerminatingAjavaProgram

score 0 · Answer 2 · answered Sep 18 '17 at 21:51

Couple of things here. First, you are working with swing, so you must access swing components on the AWT Event Dispatch Thread. There is a dispatcher you can use as part of this library. See the working with swing wiki guide on the project page.

Now on to your actual question; How to stop the loop? I see you have a loop on the event listener, which will block receiving events like F-10 until the loop finishes and the thread can continue dispatching events. You should start the F-9 process loop in its own thread and use some thread safe mechanism to signal that loop when F-10 is pressed. If you want to stop the native hook for some reason, there is a method on the GlobalScreen to unhook.

Close program with keypress during a loop

The program runs (with F9) but it doesn't stop when I press F10.

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2 Answers2