Run and pause a GUI background thread by clicking a button

Question

I need to run a background thread in my Java GUI that only runs when I click a button and pauses when I click that button again. I am not exactly sure how to set this up, but I have placed a thread in my constructor and the while loop within is set to go through when I set a specific boolean to TRUE. One button switches from setting this boolean TRUE or FALSE.

Everything else I have in this GUI works fine. When I tried debugging the thread, it actually works as I step through the thread but nothing when I try running the GUI completely. The GUI is rather large so I'm gonna put up a portion of the constructor and the action listener of the button. The rest of the code is unnecessary since it works just fine. I need to know what I am doing wrong here:

public BasketballGUI() {
    // certain labels and buttons
    Thread runningSim = new Thread() {
        public void run() {
            while(simRun) {
                // do stuff here
            }
        }
    };
    runningSim.start();
}

// other GUI stuff

// actionListener that should run the thread.
class SimButtonListener implements ActionListener {
    public void actionPerformed(ActionEvent arg0) {
        if(!simRun) {
            simRun = true;
            sim.setText("Pause Simulator");
        }
        else if(simRun) {
            simRun = false;
            sim.setText("Run Simulator");
        }
        // other stuff in this actionListener
    }
}

Answer 1

1. Establish a Swing based Timer with an ActionListener that will be called repeatedly.
2. In the actionPerformed(ActionEvent) method call repaint().
3. Start the timer (Timer.start()) when the user clicks Start
4. Stop the timer (Timer.stop()) when the user clicks Stop

If you cannot get it working from that description, I suggest you post an SSCCE of your best attempt.

---

I thought I had one 'lying around'.. Try this working SSCCE which uses images created in this SSCCE.

Answer 2

I could see this background thread useful for a Java GUI when handling button events to affect something like a text area or progress bar.

For the sake of argument, I will build you a tiny GUI that affects a Text Area. I hope this helps you.

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.concurrent.atomic.AtomicBoolean;
import javax.swing.*;

public class TestClass extends JPanel {

    super("TestClass - Title");
    private AtomicBoolean paused;
    private JTextArea jta;
    private JButton btn;
    private Thread thread;

    public TestClass() {

        paused = new AtomicBoolean(false);
        jta = new JTextArea(100, 100);
        btn = new JButton();

        initialize();
    }

    public void initialize() {

        jta.setLineWrap(true);
        jta.setWrapStyleWord(true);
        add(new JScrollPane(jta));
        btn.setPreferredSize(new Dimension(100, 100));
        btn.setText("Pause");
        btn.addActionListener(new ButtonListener());
        add(btn);

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                while(true) {

                    for(int i = 0; i < Integer.MAX_VALUE; i++) {

                        if(paused.get()) {
                            synchronized(thread) {
                                try {

                                    thread.wait();

                                } catch(InterruptedException e) {
                                }
                            }
                        }
                    }

                    jta.append(Integer.toString(i) + ", ");

               try {

                   Thread.sleep(500);

               } catch (InterruptedException e) {
                }
                }
            }
        };
        thread = new Thread(runnable);
        thread.start();
    }

    @Override
    public Dimension getPreferredSize() {

        return new Dimension(100, 30);

    }

            class ButtonListener implements ActionListener {

                @Override
                public void actionPerformed(ActionEvent event) {

                    if(!paused.get()) {
                        btn.setText("Start");
                        paused.set(true);
                    } else {
                        btn.setText("Pause");
                        paused.set(false);

                        synchronized(thread) {
                            thread.notify();
                        }
                    }
                }
            }
}

Main class to call everything.

import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class MainClass {

    public static void main(final String[] arg) {

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestClass());
                frame.pack();
                frame.setVisible(true);
                frame.setLocationRelativeTo(null);
            }
        });
    }
}

I did not test this code to see if it works exactly, Its main goal is to break you through your coders block and use my components to fix your issue. Hope this helped. Need anything else Email me at DesignatedSoftware@gmail.com