Java

Swing and threads

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Join Date: Mar 2008

Posts: 2

Reputation: renoss is an unknown quantity at this point

Solved Threads: 0

renoss

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Newbie Poster

Swing and threads

Sep 24th, 2008

Hi,
My problem is that I need to tell class A to repaint, but from class B.
Class B will be a thread that updates components of class A and will eventually tell A to repaint.
The basic idea of my code is as follows:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
class A extends JPanel{
    Thread b;
    ...
    b = new B();
 
    paint(Graphics g){
    ...
    }
}
 
class B extends A implements Runnable{
    run(){
        ...
        //Tell A to repaint
    }
}
class A extends JPanel{
    Thread b;
    ...
    b = new B();

    paint(Graphics g){
    ...
    }
}

class B extends A implements Runnable{
    run(){
        ...
        //Tell A to repaint
    }
}

From my understanding of swing, I need to tell A to repaint when referring directly to it
For example:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
class X{
    A a;
    ...
    a.repaint();
}
class X{
    A a;
    ...
    a.repaint();
}

Or I could call repaint inside of Class A

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
class A{
   ...
  repaint();
}
class A{
   ...
  repaint();
}

But how do I do this from the run() method of class B?

Thanks in advance.

•

Join Date: Jun 2008

Posts: 973

Reputation: Alex Edwards is a jewel in the rough

Solved Threads: 107

Alex Edwards Alex Edwards is offline

Offline

Posting Shark

Re: Swing and threads

Sep 24th, 2008

Why exactly does class B have to extend A?

From an immediate glance I can see a potential cycle instantiation issue.

Think about it--

1) Class A, after static initialization, will instantiate a class B object--

2) Class B extends A, so when a B object is constructed, the super constructor of A is called but between that process the pre-initialization is done again leading back to step 1!

--which means that your program will cause new memory to be called and constructors to be (in theory) pushed on stack memory along with variables that are used within them, and additional growth of objects in the heap due to subsequent calls of new that are not resolved to make objects unreachable since there is a valid reference pointing to it.

What you want to do is something like this--

 Help with Code Tags 
 java Syntax (Toggle Plain Text) 
import javax.swing.*;
 
public class NameSpaceClass001{
 
	class A extends JPanel{
 
		// blah... mumble...
		private B myB = null;
		public A(){
			myB = new B(this);
			Thread t = new Thread(myB);
			t.setDaemon(true);
			t.start();
		}
	}
 
	class B implements Runnable{
 
		private A panel = null;
		public boolean running = true;
 
		public B(A ref){
			panel = ref;
		}
 
		private int safeWait(int seconds){
			long l = System.currentTimeMillis(); // get current time
			long next = l + (seconds * 1000); // get current time + future time
			while(l < next) l = System.currentTimeMillis(); // wait specified seconds
			return seconds;
		}
 
		@Override public void run(){
			while(running){
				System.out.println("Calling repaint after " + safeWait(3) + " seconds...");
				panel.repaint();
 
			}
		}
	}
 
	public static void main(String... args){
		NameSpaceClass001 nsc001 = new NameSpaceClass001();
		nsc001.new A();
	}
}
import javax.swing.*;

public class NameSpaceClass001{

	class A extends JPanel{

		// blah... mumble...
		private B myB = null;
		public A(){
			myB = new B(this);
			Thread t = new Thread(myB);
			t.setDaemon(true);
			t.start();
		}
	}

	class B implements Runnable{

		private A panel = null;
		public boolean running = true;

		public B(A ref){
			panel = ref;
		}

		private int safeWait(int seconds){
			long l = System.currentTimeMillis(); // get current time
			long next = l + (seconds * 1000); // get current time + future time
			while(l < next) l = System.currentTimeMillis(); // wait specified seconds
			return seconds;
		}

		@Override public void run(){
			while(running){
				System.out.println("Calling repaint after " + safeWait(3) + " seconds...");
				panel.repaint();

			}
		}
	}

	public static void main(String... args){
		NameSpaceClass001 nsc001 = new NameSpaceClass001();
		nsc001.new A();
	}
}

Last edited by Alex Edwards; Sep 24th, 2008 at 3:00 am.

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Join Date: Jun 2008

Posts: 973

Reputation: Alex Edwards is a jewel in the rough

Solved Threads: 107

Alex Edwards Alex Edwards is offline

Offline

Posting Shark

Re: Swing and threads

Sep 24th, 2008

I marked the Thread daemon as a good practice. Unfortunately it makes the example hard to see, the way the code is currently written. Consider this example instead--

 Help with Code Tags 
 java Syntax (Toggle Plain Text) 
import javax.swing.*;
 
public class NameSpaceClass001{
 
	class A extends JPanel{
 
		// blah... mumble...
		private B myB = null;
		public A(){
			myB = new B(this);
			Thread t = new Thread(myB);
			t.setDaemon(true);
			t.start();
		}
 
		public B getB(){
			return myB;
		}
	}
 
	class B implements Runnable{
 
		private A panel = null;
		public boolean running = true;
 
		public B(A ref){
			panel = ref;
		}
 
		public int safeWait(int seconds){
			long l = System.currentTimeMillis(); // get current time
			long next = l + (seconds * 1000); // get current time + future time
			while(l < next) l = System.currentTimeMillis(); // wait specified seconds
			return seconds;
		}
 
		@Override public void run(){
			while(running){
				System.out.println("Calling repaint after " + safeWait(3) + " seconds...");
				panel.repaint();
 
			}
		}
	}
 
	public static void main(String... args){
		NameSpaceClass001 nsc001 = new NameSpaceClass001();
		NameSpaceClass001.A myA = nsc001.new A();
 
		myA.getB().safeWait(15);
	}
}
import javax.swing.*;

public class NameSpaceClass001{

	class A extends JPanel{

		// blah... mumble...
		private B myB = null;
		public A(){
			myB = new B(this);
			Thread t = new Thread(myB);
			t.setDaemon(true);
			t.start();
		}

		public B getB(){
			return myB;
		}
	}

	class B implements Runnable{

		private A panel = null;
		public boolean running = true;

		public B(A ref){
			panel = ref;
		}

		public int safeWait(int seconds){
			long l = System.currentTimeMillis(); // get current time
			long next = l + (seconds * 1000); // get current time + future time
			while(l < next) l = System.currentTimeMillis(); // wait specified seconds
			return seconds;
		}

		@Override public void run(){
			while(running){
				System.out.println("Calling repaint after " + safeWait(3) + " seconds...");
				panel.repaint();

			}
		}
	}

	public static void main(String... args){
		NameSpaceClass001 nsc001 = new NameSpaceClass001();
		NameSpaceClass001.A myA = nsc001.new A();

		myA.getB().safeWait(15);
	}
}