StackOverflowError when trying to use threads

[Krysten Thomas]

I am currently working on a project that is basically a projectile motion simulation with a user interface.
The original version did not use any threads and simply took the data that was entered in by the user and performed the computations on that data in order to run the simulation.
Well the program would run incredibly slow and sometimes crash. After some research, I realized I had to use a new thread to handle the computations that was slowing down the program.

But now when I run the new version of the program, I get a StackOverflowError. I believe these sorts of errors have to do with infinitely running loops, and loops that are never exited?
But the while loop that I have has a condition that should exit itself.

Why am I getting this error, and how could I go about resolving the issue?

Here is the code:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import javax.swing.*;
import net.miginfocom.swing.MigLayout;

public class SimulationGUI implements ActionListener, Runnable
{
	private JFrame window;
	private JPanel leftPanel, rightPanel, topPanel; 
	private JLabel range, heightT, time, conditions, angle, speed, mass;
	private JLabel height, coeff, epsilonx, epsilony, acceleration, accx, accy;
	private JTextField rangeText, heightTText, timeText, angleText, speedText, massText, heightText;
	private JTextField epxText, epyText, accxText, accyText; 
	private JButton start, erase; 

	SimulationGUI()
	{
                //Create window
		window = new JFrame("Projectile Motion");
		window.setSize(1200, 700); 
		window.setLayout(new MigLayout());
		window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		//Create left panel
		leftPanel = new JPanel();
		leftPanel.setLayout(new MigLayout("alignx center")); 
		leftPanel.setBackground(Color.cyan);
		window.add(leftPanel, "width 900, height 700"); 

		//Create top panel in left panel
		topPanel = new JPanel();
		topPanel.setLayout(new MigLayout("alignx center")); 
		topPanel.setBackground(Color.cyan);
		leftPanel.add(topPanel, "width 1000, height 50");

		//Creates top panel labels and text fields that will display time, numBounces, and maxHeight
		range = new JLabel("Range (m): ");
		topPanel.add(range); 	
		rangeText = new JTextField(); 
		topPanel.add(rangeText, "width 200, height 20px, gapafter 20");  //Sets size of button to be 20 px by 20px

		heightT = new JLabel("Height (m): ");
		topPanel.add(heightT); 	
		heightTText = new JTextField(); 
		topPanel.add(heightTText, "width 200, height 20px, gapafter 20");  //Sets size of button to be 20 px by 20px

		time = new JLabel("Time (s): ");
		topPanel.add(time);
		timeText = new JTextField(); 
		topPanel.add(timeText, "width 200, height 20px, gapafter 20");  //Sets size of button to be 20 px by 20px

		//Create right panel
		rightPanel = new JPanel(new MigLayout());
		rightPanel.setBackground(Color.yellow); 
		window.add(rightPanel, "width 300, height 700");

		//Create right panel labels and textfields for right panel
		conditions = new JLabel("Initial Conditions: ");
		rightPanel.add(conditions, "width 50, height 50, wrap, gapleft 85");

		angle = new JLabel("Angle (degrees)"); 
		rightPanel.add(angle, "width 50, height 50"); 
		angleText = new JTextField(); 
		rightPanel.add(angleText, "width 70, height 10, wrap"); 

		speed = new JLabel("Initial Speed (m/s)"); 
		rightPanel.add(speed, "width 50, height 50");
		speedText = new JTextField(); 
		rightPanel.add(speedText, "width 70, height 10, wrap");

		mass = new JLabel("Mass (kg)"); 
		rightPanel.add(mass, "width 50, height 50"); 
		massText = new JTextField(); 
		rightPanel.add(massText,  "width 70, height 10, wrap");

		height = new JLabel("Initial Height (m)");
		rightPanel.add(height, "width 50, height 50");
		heightText = new JTextField();
		rightPanel.add(heightText, "width 70, height 10, wrap");

		coeff = new JLabel("Coeffcient of Restitution"); 
		rightPanel.add(coeff, "width 50, height 50, wrap");

		epsilonx = new JLabel("In Horizontal Direction");
		rightPanel.add(epsilonx, "width 50, height 50");
		epxText = new JTextField();
		rightPanel.add(epxText, "width 70, height 10, wrap");

		epsilony = new JLabel("In Vertical Direction");
		rightPanel.add(epsilony, "width 50, height 50");
		epyText = new JTextField();
		rightPanel.add(epyText, "width 70, height 10, wrap");

		acceleration = new JLabel("Acceleration"); 
		rightPanel.add(acceleration, "width 50, height 50, wrap");

		accx = new JLabel("In Horizontal Direction");
		rightPanel.add(accx, "width 50, height 50");
		accxText = new JTextField();
		rightPanel.add(accxText, "width 70, height 10, wrap");

		accy = new JLabel("In Vertical Direction");
		rightPanel.add(accy, "width 50, height 50");
		accyText = new JTextField();
		rightPanel.add(accyText, "width 70, height 10, wrap");

		//Create start button
		start = new JButton("Start!"); 
		start.setForeground(Color.white); 
		start.setBackground(Color.red); 
		rightPanel.add(start, "width 90, height 30"); 

		//Create erase button
		erase = new JButton("Erase!");
		erase.setForeground(Color.white); 
		erase.setBackground(Color.blue); 
		rightPanel.add(erase, "width 95, height 30"); 

		//Add action listeners for each text field
		ActionListener angleList = new SimulationGUI(); 
		angleText.addActionListener(angleList);  

		ActionListener speedList = new SimulationGUI();
		speedText.addActionListener(speedList); 

		ActionListener massList = new SimulationGUI();
		massText.addActionListener(massList);

		ActionListener heightList = new SimulationGUI();
		heightText.addActionListener(heightList); 

		ActionListener epxList = new SimulationGUI();
		epxText.addActionListener(epxList); 

		ActionListener epyList = new SimulationGUI();
		epyText.addActionListener(epyList); 

		ActionListener accxList = new SimulationGUI(); 
		accxText.addActionListener(accxList); 

		ActionListener accyList = new SimulationGUI();
		accyText.addActionListener(accyList);

		ActionListener startButton = new SimulationGUI();
		start.addActionListener(startButton); 
	}

	public void actionPerformed(ActionEvent e)
	{

		Thread thread = new Thread(this);
		thread.start();  // this calls the method run()
	}

	public void run()
	{
		double angle = Double.valueOf(angleText.getText());
		double vel = Double.valueOf(speedText.getText()); 
		double mass = Double.valueOf(massText.getText()); 
		double y = Double.valueOf(heightText.getText());
		double x = 30;
		double epX = Double.valueOf(epxText.getText());
		double epY = Double.valueOf(epyText.getText());
		double ax = Double.valueOf(accxText.getText());
		double ay = Double.valueOf(accyText.getText()); 

		int numBounces = 0;
		double deltaTime = .00000001; 
		double total_velocity = 0.0;
		double time = 0.0;

		while(numBounces < 10)
		{
			//Increment Time
			time = time + deltaTime;

			//Calculate new values for velocity[x] and velocity[y]
			double vx = vel*Math.cos(angle) + ax*time;
			double vy = vel*Math.sin(angle )+ ay*time; 

			//Calculate new values for x and y
			x = x + vx*time;
			y = y + vy*time + .5*ay*(time*time);

			rangeText.setText(" " + x);
			heightTText.setText(" " + y); 
			timeText.setText(" " + time);

			//Draw projectile

			//If ball hits ground: y < 0
			if(y < 0)
			{
				numBounces++;

				System.out.println("Number of Bounces: " + numBounces); 

				//Calculate new velocity
				vy = -vy - ay*time; 

				//Calculate angle
				angle = Math.atan(vy/vx);

				//Calculate total velocity
				total_velocity = Math.sqrt((vy*vy) + (vx*vx));

				//Velocity with elasticity factored in
				total_velocity = Math.sqrt((epY) * total_velocity); 

				//New velocities for when ball makes next trip
				vy = total_velocity*Math.sin(angle); 
				vx = total_velocity*Math.cos(angle);

				rangeText.setText(" " + x);
				heightTText.setText(" " + y); 
				timeText.setText(" " + time);

				//Draw projectile
			}
		}
	}

	public static void main(String[] args)
	{
		new SimulationGUI(); 
	}

}

And here are the errors that I am getting:

Exception in thread "main" java.lang.StackOverflowError
	at java.awt.Insets.<init>(Unknown Source)
	at sun.awt.windows.WToolkit.getScreenInsets(Native Method)
	at sun.awt.windows.WToolkit.getScreenInsets(Unknown Source)
	at java.awt.Window.init(Unknown Source)
	at java.awt.Window.<init>(Unknown Source)
	at java.awt.Frame.<init>(Unknown Source)
	at javax.swing.JFrame.<init>(Unknown Source)
	at SimulationGUI.<init>(SimulationGUI.java:23)
	at SimulationGUI.<init>(SimulationGUI.java:124)
                                         .
                                         .
                                         .
                                         .
                                         .

[Chris Hurst]

Its massively recursive ...

To create a SimulationGUI it must create a SimulationGUI which creates a SimulationGUI ..... > to infinity or you run out of stack RAM !

in ctr (example), you can't have a line like this it'll call itself to infinity , you probably meant to use 'this' but that's a bad idea as well ;-) ...

 ActionListener massList = new SimulationGUI();  

other problems (ignore these if your just playing) ...

You should really do as little as possible in the ctr, you really want your EDT variables to be final but don't register listeners in a ctr, have a create method and call it on the EDT.

In your run thread any interaction with the GUI you need to get onto the EDT thread see java SwingWorker, you shouldn't change the GUI on your thread.

[Krysten Thomas]

Ok so I added a new method called createListeners() that will create the action listeners for the various text fields and buttons that I have.

	public void createListeners()
	{
		//Add action listeners for each text field
		ActionListener angleList = new SimulationGUI(); 
		angleText.addActionListener(angleList);  

		ActionListener speedList = new SimulationGUI();
		speedText.addActionListener(speedList); 

		ActionListener massList = new SimulationGUI();
		massText.addActionListener(massList);

		ActionListener heightList = new SimulationGUI();
		heightText.addActionListener(heightList); 

		ActionListener epxList = new SimulationGUI();
		epxText.addActionListener(epxList); 

		ActionListener epyList = new SimulationGUI();
		epyText.addActionListener(epyList); 

		ActionListener accxList = new SimulationGUI(); 
		accxText.addActionListener(accxList); 

		ActionListener accyList = new SimulationGUI();
		accyText.addActionListener(accyList);

		ActionListener startButton = new SimulationGUI();
		start.addActionListener(startButton); 
	}

And I call it in my SimulationGUI() constructor at the very end
I have also temporarily commented out the code that sets the text in my run method.
Here is the new error that I am getting:

Exception in thread "main" java.lang.NullPointerException
	at SimulationGUI.<init>(SimulationGUI.java:26)
	at SimulationGUI.main(SimulationGUI.java:232)

Now in regards to not changing the GUI in my run() method.
Are you referring to where I set the text of my textfields?

			rangeText.setText(" " + x);
			heightTText.setText(" " + y); 
			timeText.setText(" " + time);

Would I have to use a new thread for that? Or could I simply create a new method to set those text fields and call it in my run method.

[Chris Hurst]

Your creating a lot of simulation GUI's is that intended or should you just have one ? I suspect one is better, but then you'd need to determine the component initiating an action in the listener. To be honest looking at the code I'd recommend you do a few simple swing tutorials first, then come back to me for the threading.

These next two points are viild but I'd ignore them and sort out the issues above first ...

The reasons for doing the next two are complex so unless you really need to know I suggest you just do the following ..

1) You have a thread to set your text on already its the EDT (Event Dispatch Thread), lookup a tutorial on SwingUtilities invokeAndWait and InvokeLater your GUI updates should be driven this way.

2) As for construct then create, it should probably look more like this ..

public static void main(String[] args)  
    {  
        SimulationGUI gui = new SimulationGUI();   
        gui.create();
    }  

[Krysten Thomas]

Ok so basically, I need a SwingUtilities.invokeLater to update the text fields and I need a Swing Worker to handle the time consuming calculations in my program?

[Bernhard Haeussermann]

Look at what you're doing in the constructor. For each GUI component that listens for events, you're creating a completely separate SimulationGUI object on which it listens, which is extremely wasteful. Furthermore, in the code

ActionListener angleList = new SimulationGUI();

you call the constructor again. But then within that constructor-call this line is executed again and the constructor is called again. In this process of infinite recursion the run-time stack grows and grows until it overflows.

All the GUI components should probably listen for events from the same single SimulationGUI object. That is, in the original code that you posted, you should change

ActionListener angleList = new SimulationGUI();

to

ActionListener angleList = this;

and similar for the other calls to addActionListener().

However, it is evident that you don't really get how the event handling of Swing works. First make sure that you really grasp what's going on in this code.

[Krysten Thomas]

So I understand that my original code had infinite recursion. I've changed that part completely.
My action listeners are now (for example): button.addActionListener(this);
But my program still lags significantly and actually it become unresponsive, only running through one iteration of the loop I have in place, and I believe it's the time consuming calculations that I have going on in my code.

My original question is should I put the code that deals with the simulation inside a spring worker, since spring workers can handle time consuming activities, and put the code that updates the gui (the setting of the text) into a swing utilities invoke later, since that is a direct call to the EDT, and you said that any code that changes the GUI should be invoked on the EDT thread?

[Bernhard Haeussermann]

Running a very time consuming operation in an event listener's code will make the GUI unresponsive. The GUI will not respond until the call to actionPerformed() (or whatever may be the case) returns. So, yes, using a spring worker should make the UI more responsive. I believe that's the type of situation that a spring worker is intended to handle.

[Krysten Thomas]

Because right now, I have a thread to handle the simulation code, but I guess it doesn't matter if the code is on its separate thread because it still is unresponsive.
So I will try using a spring worker for that. But how can you tell by looking at the code, whether something is going to be time consuming, because all I really have are calculations, nothing extra fancy.
However, I do ultimately want to draw a line that depicts the actual projectile. So maybe, I should just implement the code into a spring worker, so that when I do add in the animation, I won't have to worry about it.

See below:

{   
        double angle = Double.valueOf(angleText.getText());   
        double vel = Double.valueOf(speedText.getText());    
        double mass = Double.valueOf(massText.getText());    
        double y = Double.valueOf(heightText.getText());   
        double x = 30;   
        double epX = Double.valueOf(epxText.getText());   
        double epY = Double.valueOf(epyText.getText());   
        double ax = Double.valueOf(accxText.getText());   
        double ay = Double.valueOf(accyText.getText());    
  
        int numBounces = 0;   
        double deltaTime = .00000001;    
        double total_velocity = 0.0;   
        double time = 0.0;   
  
        while(numBounces < 10)   
        {   
            //Increment Time   
            time = time + deltaTime;   
  
            //Calculate new values for velocity[x] and velocity[y]   
            double vx = vel*Math.cos(angle) + ax*time;   
            double vy = vel*Math.sin(angle )+ ay*time;    
  
            //Calculate new values for x and y   
            x = x + vx*time;   
            y = y + vy*time + .5*ay*(time*time);   
  
            //Draw projectile   
  
            //If ball hits ground: y < 0   
            if(y < 0)   
            {   
                numBounces++;   
  
                System.out.println("Number of Bounces: " + numBounces);    
  
                //Calculate new velocity   
                vy = -vy - ay*time;    
  
                //Calculate angle   
                angle = Math.atan(vy/vx);   
  
                //Calculate total velocity   
                total_velocity = Math.sqrt((vy*vy) + (vx*vx));   
  
                //Velocity with elasticity factored in   
                total_velocity = Math.sqrt((epY) * total_velocity);    
  
                //New velocities for when ball makes next trip   
                vy = total_velocity*Math.sin(angle);    
                vx = total_velocity*Math.cos(angle);  

[Bernhard Haeussermann]

Yes, I would suggest that you use a spring worker, so that you draw a line on the UI.

Initially, you can limit the number of iterations of the main loop to, say 100, and then plot the points to see what it looks like and continue from there.

[Krysten Thomas]

The main loop meaning the while loop that I have? What do you mean limit the number of iterations to 100?

[Bernhard Haeussermann]

I mean the loop with the condition (numBounces < 10).
I meant that you limit the number of iterations of this loop to say 100. You could do this by replacing

while (numBounces<10)

by

for (int i=0; (numBounces<10) && (i<100); i++)

just to get a feel for what's going on.

[Krysten Thomas]

But don't both conditions have to be true for the loop to exit ie. numBounces has to be less than 10 and i < 100
So the loop would still take the same amount of time?

[Bernhard Haeussermann]

No, if either condition becomes false the loop will exit.

[Krysten Thomas]

oh ok i see.

Thanks for the help