Stopping and starting thread for multiple key clicks

[Ben Watt]

I have a thread that calls repaint() which draws a character jumping using certain images.

I press the space bar to make the character jump and whatnot.


I'm using a loop and a try-catch statement to keep track of which image I want drawn.

My problem is, I need the thread to stop going, so that when I move the character, I can jump again, but it says "IllegalThreadStateException" and highlights the "clockThread.start()" line of when I press the Space key.


It makes sense, because I never put a statement to stop it anywhere, and it can't start again.

I need to know where I can stop the thread, at what point?

And also - everywhere I put it, I get a "Supress warning for 'deprecation'"

Any help is appreciated. I can post code as well but it'll take about a day.

[Henry Wong]

First of all, stopping a thread is deprecated. There are some race conditions related to stopping a thread that can leave internal JVM variables in an unwanted state -- don't use it. Second, even if stop() was allowed, you can't restart the thread via the start() method. It is just not allowed.

I am assuming by stop and start, you want the other thread to wait for the first thread. to get some stuff done before it goes and does some work. The way to do this is cooperatively.... You actually have to code the other thread to wait for your first thread, to sychronize between the two threads, and to use notifications to trigger each other, etc.

Henry

[Henry Wong]

And BTW, Swing (and AWT) has some threading requirements -- so, you may have to explain a bit more, as not all operations are allowed in any thread.

Henry

[Alan Mehio]

Ben Watt wrote:I have a thread that calls repaint() which draws a character jumping using certain images..

You are not allowed to create thread which calls the Swing component to do rendering but rather you put such a request for repaint on the
EventDispatchThread. Swing event handling code runs on a special thread known as the event dispatch thread. Most code that invokes Swing methods also runs on this thread. Most of the Swing method are not thread safe.

ex:

   

SwingUtilities.invokeLater(new Runnable() {  //Note 1
            public void run() {
               // your code here
            }
        });

// the above will call the run method inside the EventDispatchThread

 

Ben Watt wrote:

I press the space bar to make the character jump and whatnot.


I'm using a loop and a try-catch statement to keep track of which image I want drawn.

My problem is, I need the thread to stop going, so that when I move the character, I can jump again, but it says "IllegalThreadStateException" and highlights the "clockThread.start()" line of when I press the Space key.


It makes sense, because I never put a statement to stop it anywhere, and it can't start again.

I need to know where I can stop the thread, at what point?

And also - everywhere I put it, I get a "Supress warning for 'deprecation'"

Any help is appreciated. I can post code as well but it'll take about a day.

You need to do something like; Foo will have a reference to the swing object which is not seen below

  


public class Foo implements Runnable {
	private Object object = new Object();
	private boolean interrupt = false;
	private volatile boolean stop = false;

	public void run() {
		while (!interrupt) {

			while (!stop && !interrupt) {
				synchronized (object) {
					System.out.println(System.currentTimeMillis());
					// do something and put it on event dispatch
					try {
						if (stop)
							object.wait();
					} catch (InterruptedException inter) {
						Thread.currentThread().isInterrupted(); // state change
																// to inform the
																// caller
					}
				}
			}
		}
	}

	public void stop() {
		System.out.println("stop now");
		stop = true;
	}

	public void resum() {
		System.out.println("resume now");
		stop = false;
		synchronized (object) {
			object.notify();
		}
	}

	public void interrup() {
		System.out.println("interrupted now");
		interrupt = true;
	}
}








public class SwingActivity {
	
	private Foo foo;
	
	public SwingActivity(Foo foo) {
		this.foo = foo;
	}

	public  void stopThread() {
		foo.stop();
	}
	
	public void resumThread() {
		foo.resum();
	}
	
	public void interrupThread() {
		foo.interrup();
	}
	
	
	
	public static void main(String args[]) throws InterruptedException {
		Foo foo = new Foo();
		SwingActivity activity = new SwingActivity(foo);
		Thread thread = new Thread(foo);
		thread.start();
		
		 Thread.currentThread().sleep(5000); // simulate some activities
		 
		 activity.stopThread(); // press stop button
		 
		 Thread.sleep(2000);
		 
		 activity.resumThread(); // press resume button 
		 
		 Thread.sleep(1000);
		 
		 activity.interrupThread(); // terminate the thread or the activity 
	}
	
}


 

Hope this could help

[Henry Wong]

Alan Mehio wrote:

Ben Watt wrote:I have a thread that calls repaint() which draws a character jumping using certain images..

You are not allowed to create thread which calls the Swing component to do rendering but rather you put such a request for repaint on the
EventDispatchThread. Swing event handling code runs on a special thread known as the event dispatch thread. Most code that invokes Swing methods also runs on this thread. Most of the Swing method are not thread safe.

ex: ....

Actually, the repaint() method is one of the few exceptions to this rule. You can actually request a repaint, by calling the repaint() method, from any thread.

Henry

[Alan Mehio]

Henry Wong wrote:

Alan Mehio wrote:

Ben Watt wrote:I have a thread that calls repaint() which draws a character jumping using certain images..

You are not allowed to create thread which calls the Swing component to do rendering but rather you put such a request for repaint on the
EventDispatchThread. Swing event handling code runs on a special thread known as the event dispatch thread. Most code that invokes Swing methods also runs on this thread. Most of the Swing method are not thread safe.

ex: ....

Actually, the repaint() method is one of the few exceptions to this rule. You can actually request a repaint, by calling the repaint() method, from any thread.

Henry

Henry,
Thanks for your comment. Yes I see your point plus the revalidate(), and invalidate() methods which I missed to mention.

[Ben Watt]

All of this has been very helpful.

I am a first year java programmer and have a hard time understanding much of what y'all are saying.

Here is the code I used for my program, hopefully this is more informative than my shoddy explanation to start with.



To repeat, All I want to do is reset the Thread and have it start again each time I click the Space key.

package Final;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.ImageIcon;
import javax.swing.JFrame;

public class Level1 extends JFrame implements KeyListener, MouseListener, Runnable{

	static Thread clockThread;
	boolean keyRight = false;
	boolean keyLeft = false;
	boolean keySpace = false;
	boolean lastRight = false;
	boolean lastLeft = false;
	int t = 0;
	int xpos = 0;
	int ypos = 0;
	Image man = new ImageIcon("Stickman.png").getImage();

	public Level1(){
		//Code that sizes and sets all properties of the window and adds Listeners for Key and Mouse.
		clockThread = new Thread(this);
	}

	public static void main(String[] args){
		Level1 window = new Level1();
		window.setExtendedState(MAXIMIZED_BOTH);
		window.setVisible(true);
		window.repaint();
	}

	public void paint(Graphics g){

		super.paint(g);

		if(keyRight == true){
			g.drawImage(man, xpos, ypos, null);
			xpos += 5;
		}else if(keyLeft == true){
			g.drawImage(man, xpos, ypos, null);
			xpos -= 5;
		}else if(keySpace == true){
			if(lastLeft == true){
				/*Switch statement that relies on the values of 't' to determine which image to draw in a given direction. There is also a statement to set keySpace and lastRight to false.*/
			}else if(lastRight == true){
				/*Switch statement much like above, except the direction of the jump is changed. There is also a statement to set keySpace and lastRight to false.*/
			}
		}

		keyRight = false; 
		keyLeft = false;

	}

	public void keyPressed(KeyEvent e) {

		if(e.getKeyCode() == KeyEvent.VK_RIGHT){
			keyRight = true;
			lastRight = true;
			repaint();
		}else if(e.getKeyCode() == KeyEvent.VK_LEFT){
			keyLeft = true;
			lastLeft = true;
			repaint();
		}else if(e.getKeyCode() == KeyEvent.VK_SPACE){
			keySpace = true;
			clockThread.start();
		}

	}

	public void run() {
		while(t < 5){
			try {
				clockThread.sleep(250);
				repaint();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			t++;
		}
		t = 0;
	}
}    

And if there are any other general programming etiquette problems, I'd appreciate the help.

[Henry Wong]

Instead of the space key being used to start / stop the thread -- why don't you start the thread right away. And key that thread running.

You can modify the thread to check a flag to decide whether to call the repaint method. And then you can change your key listener to toggle that flag.

Henry