Don't really know where to go...

Question

Hey there fellas....
I've got quite a weird series of problems on my hands, so I'm hoping you can help.
Basically, my whole program won't repaint, and therefore I can't really tell what the hell is going on... anyway, here goes the whole thing....
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import java.lang.Math.*;
public class EMGame extends JFrame {
// various panes I'll need to display stuff
JPanel toppanel = null;
SimPanel simulation = null;
JPanel partsbin = null;
JPanel properties = null;
JMenuBar menubar = null;
JMenu filemenu = null;
JMenu simmenu = null;
Vector PtChargeList = null;
String ItemOnCursor = null;
JButton PtChargeButton = null;
PtCharge SelectedCharge = null;
boolean simulating = false;
JTextField ChargeProp = null;
JTextField MassProp = null;
JTextField xPosBox = null;
JTextField yPosBox = null;
JTextField zPosBox = null;
JLabel ChargePropLabel = null;
JLabel MassPropLabel = null;
JLabel xPosBoxLabel = null;
JLabel yPosBoxLabel = null;
JLabel zPosBoxLabel = null;
// main program that calls the function
public static void main(String args[]) {
EMGame game = new EMGame();
public EMGame() {
setTitle("Electricity and Magnetism Game");
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
PtChargeList = new Vector(10);
PtChargeList.add(0,new PtCharge(100,100,0,0,0,0, 2, 1e-30));
PtChargeList.add(1,new PtCharge(200,100,0,0,0,0,2,1e-30));
PtChargeList.add(2,new PtCharge(150,100,0,0,10,0,-8,1e-30));
PtChargeList.add(3,new PtCharge(150,120,0,10,10,0,0,1e-30));
JMenuItem menuitem;
// creating the panes
toppanel = new JPanel(new BorderLayout());
simulation = new SimPanel();
simulation.setBackground(Color.yellow);
simulation.setPreferredSize(new Dimension(700,700));
partsbin = new JPanel(new GridLayout());
partsbin.setBackground(Color.black);
partsbin.setPreferredSize(new Dimension(800,100));
PtChargeButton = new JButton("Point Charge");
PtChargeButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
ItemOnCursor = "PtCharge";
} // end actionPerformed
} // end ActionListener
partsbin.add(PtChargeButton);
properties = new JPanel(new GridLayout(20,1));
properties.setBackground(Color.white);
properties.setPreferredSize(new Dimension(100,700));
ChargeProp = new JTextField("Charge");
ChargeProp.setEditable(false);
MassProp = new JTextField("Mass");
MassProp.setEditable(false);
xPosBox = new JTextField("x-position");
xPosBox.setEditable(false);
yPosBox = new JTextField("y-position");
yPosBox.setEditable(false);
zPosBox = new JTextField("z-position");
zPosBox.setEditable(false);
ChargePropLabel = new JLabel("Charge:");
MassPropLabel = new JLabel("Mass:");
xPosBoxLabel = new JLabel("x-Position");
yPosBoxLabel = new JLabel("y-Position");
zPosBoxLabel = new JLabel("z-Position");
properties.add(ChargePropLabel);
properties.add(ChargeProp);
properties.add(MassPropLabel);
properties.add(MassProp);
properties.add(xPosBoxLabel);
properties.add(xPosBox);
properties.add(yPosBoxLabel);
properties.add(yPosBox);
properties.add(zPosBoxLabel);
properties.add(zPosBox);
menubar = new JMenuBar();
setJMenuBar(menubar);
filemenu = new JMenu("File");
filemenu.setMnemonic(KeyEvent.VK_F);
filemenu.getAccessibleContext().setAccessibleDescription("");
menubar.add(filemenu);
simmenu = new JMenu("Simulation");
simmenu.setMnemonic(KeyEvent.VK_S);
simmenu.getAccessibleContext().setAccessibleDescription("Simulation Options");
menubar.add(simmenu);
menuitem = new JMenuItem("Quit", KeyEvent.VK_Q);
menuitem.setAccelerator(KeyStroke.getKeyStroke(
KeyEvent.VK_Q, ActionEvent.CTRL_MASK));
menuitem.getAccessibleContext().setAccessibleDescription(
"Leaves the Program");
menuitem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.exit(0);
} // end actionPerformed
} // end ActionListener
filemenu.add(menuitem);
menuitem = new JMenuItem("Go!!!", KeyEvent.VK_G);
menuitem.setAccelerator(KeyStroke.getKeyStroke(
KeyEvent.VK_G, ActionEvent.CTRL_MASK));
menuitem.getAccessibleContext().setAccessibleDescription(
"Starts the Simulation");
menuitem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
simulating=true;
simulate();
toppanel.repaint();
} // end actionPerformed
} // end ActionListener
simmenu.add(menuitem);
menuitem = new JMenuItem("Stop!!!", KeyEvent.VK_S);
menuitem.setAccelerator(KeyStroke.getKeyStroke(
KeyEvent.VK_S, ActionEvent.CTRL_MASK));
menuitem.getAccessibleContext().setAccessibleDescription(
"Stops the Simulation");
menuitem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
simulating=false;
toppanel.repaint();
} // end actionPerformed
} // end ActionListener
simmenu.add(menuitem);
/* Adding the parts together like this:
* ---------+
* | | |
* | | |
* ---------+
* | |
toppanel.add(menubar, BorderLayout.NORTH);
toppanel.add(simulation, BorderLayout.CENTER);
toppanel.add(partsbin, BorderLayout.SOUTH);
toppanel.add(properties, BorderLayout.EAST);
getContentPane().add(toppanel);
pack();
setVisible(true);
} // end EMGame Constructor
private void simulate(){
while(simulating){
for(int i=0; i<PtChargeList.size(); i++) {
if(PtChargeList.get(i) != null){
((PtCharge) PtChargeList.get(i)).calculate(.01);
} // end if
} // end for
} // end while
} // end simulate()
public class SimPanel extends JPanel implements MouseInputListener {
private Vector PartsOnScreen = new Vector(10);
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
for(int i=0; i<(PtChargeList.size()); i++) {
PtCharge tmp = (PtCharge)PtChargeList.get(i);
if(tmp != null) {
PartsOnScreen.add(i,new Ellipse2D.Double(tmp.x, tmp.y, 10, 10));
} // end if
} // end for
for(int i=0; i<(PartsOnScreen.size()); i++) {
if(PartsOnScreen.get(i) != null) {
// color if's
int tmpcharge = ((PtCharge)PtChargeList.get(i)).charge;
if(tmpcharge > 0){
g2.setPaint(Color.blue);
} else if(tmpcharge < 0) {
g2.setPaint(Color.red);
} else {g2.setPaint(Color.gray);} // end color if's
g2.fill((Ellipse2D)PartsOnScreen.get(i));
} // end if
} // end for
} // end paintComponent
public void mouseClicked(MouseEvent e) {
// for loop to check if you clicked any charges
for(int i=0; i<(PartsOnScreen.size()); i++) {
// finds out if you clicked on a specific charge
if(((Ellipse2D)PartsOnScreen.get(i)).contains(e.getX(),e.getY())){
// if so, makes that the Selected Charge
SelectedCharge=(PtCharge)PtChargeList.get(i);
ChargeProp.setEditable(true);
ChargeProp.setText(""+SelectedCharge.charge);
ChargeProp.setEditable(SelectedCharge.getEditable());
MassProp.setEditable(true);
MassProp.setText(""+SelectedCharge.mass);
MassProp.setEditable(SelectedCharge.getEditable());
xPosBox.setEditable(true);
xPosBox.setText(""+SelectedCharge.x);
xPosBox.setEditable(SelectedCharge.getEditable());
yPosBox.setEditable(true);
yPosBox.setText(""+SelectedCharge.y);
yPosBox.setEditable(SelectedCharge.getEditable());
zPosBox.setEditable(true);
zPosBox.setText(""+SelectedCharge.z);
zPosBox.setEditable(SelectedCharge.getEditable());
} // end if
} // end for
if(ItemOnCursor!=null){
PtChargeList.add(new PtCharge(e.getX(),e.getY(),0,0,0,0,1,1e-30));
} // end if(ItemOnCursor!=null)
repaint();
public void mouseDragged(MouseEvent e) {
public void mousePressed(MouseEvent e){}
public void mouseMoved(MouseEvent e){}
public void mouseExited(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
public void mouseReleased(MouseEvent e){}
} // end SimPanel
public class PtCharge /* extends Part */ {
// the mass and charge of the particle
int charge;
double mass;
// loc[6] = [x1, y1, z1], vel[3] = [Vx, Vy, Vz]
double x, y, z, Vx, Vy, Vz;
// a variable which tells it whether it moves when running simulation
private boolean CanMove;
// whether settings can be changed
private boolean CanEditSettings;
/* constructor:
* should take in arrays of points, the charge, and settings
* should assign those inputs appropriately
public PtCharge(double x, double y, double z,
double Vx, double Vy, double Vz,
int charge, double mass){
// setting the variables
this.charge=charge;
this.x=x;
this.y=y;
this.z=z;
this.Vx=Vx;
this.Vy=Vy;
this.Vz=Vz;
this.mass=mass;
this.CanMove=true;
this.CanEditSettings=true;
} // end constructor
// should calculate the next position
public void calculate(double step) {
double k1[]=null;
double k2[]=null;
double k3[]=null;
double k4[]=null;
double l1[]=null;
double l2[]=null;
double l3[]=null;
double l4[]=null;
//for(int i=0;i<3;i++)
k1[0]=step*Vx;
k1[1]=step*Vy;
k1[2]=step*Vz;
l1=force(x,y,z,Vx,Vy,Vz);
l1[0]*=step;
l1[1]*=step;
l1[2]*=step;
k2[0]=step*(Vx+l1[0]/2);
k2[1]=step*(Vy+l1[1]/2);
k2[2]=step*(Vz+l1[2]/2);
l2=force(x+k1[0]/2,y+k1[1]/2,z+k1[2]/2,Vx+l1[0]/2,Vy+l1[1]/2,Vz+l1[2]/2);
l2[0]*=step;
l2[1]*=step;
l2[2]*=step;
k3[0]=step*(Vx+l2[0]/2);
k3[1]=step*(Vy+l2[1]/2);
k3[2]=step*(Vz+l2[2]/2);
l3=force(x+k2[0]/2,y+k2[1]/2,z+k2[2]/2,Vx+l2[0]/2,Vy+l2[1]/2,Vz+l2[2]/2);
l3[0]*=step;
l3[1]*=step;
l3[2]*=step;
k4[0]=step*(Vx+l3[0]);
k4[1]=step*(Vy+l3[1]);
k4[2]=step*(Vz+l3[2]);
l4=force(x+k3[0],y+k3[1],z+k3[2],Vx+l3[0],Vy+l3[1],Vz+l3[2]);
l4[0]*=step;
l4[1]*=step;
l4[2]*=step;
// updating the x's, y's, z's
x+=k1[0]/6+k2[0]/3+k3[0]/3+k4[0]/6;
y+=k1[1]/6+k2[1]/3+k3[1]/3+k4[1]/6;
z+=k1[2]/6+k2[2]/3+k3[2]/3+k4[2]/6;
//updating Vx's, Vy's, Vz's
Vx+=l1[0]/6+l2[0]/3+l3[0]/3+l4[0]/6;
Vy+=l1[1]/6+l2[1]/3+l3[1]/3+l4[1]/6;
Vz+=l1[2]/6+l2[2]/3+l3[2]/3+l4[2]/6;
} // end move
private double[] force(double x, double y, double z, double Vx, double Vy, double Vz){
final double k = 8987551787.3683;
// the components of the B-field at the point charge (x,y,z)
double Bx=0, By=0, Bz=0;
double Ex=0, Ey=0, Ez=0;
double f[]=null;
for(int i=0; i<PtChargeList.size(); i++){
// a temporary variable that is used to simplify code below
PtCharge tmp = (PtCharge)PtChargeList.get(i);
// the distance beween the current point charge and the other one, cubed
double denom = Math.pow((tmp.x-x)*(tmp.x-x)+(tmp.y-y)*(tmp.y-y)+(tmp.z-z)*(tmp.z-z), 1.5);
// B = (mu0/4pi)*q (v X (r-r1))/|r-r1|^3
Bx+=(tmp.charge)/10000000*((tmp.Vz*(y-tmp.y))+(tmp.Vy*(tmp.z-z)))/denom;
By+=(tmp.charge)/10000000*((tmp.Vz*(tmp.x-x))+(tmp.Vx*(z-tmp.z)))/denom;
Bz+=(tmp.charge)/10000000*((tmp.Vy*(x-tmp.x))+(tmp.Vx*(tmp.y-y)))/denom;
// E = k*q/r^2 rhat = kq/r^3 *r
Ex+=k*tmp.charge/denom*(tmp.x-x);
Ey+=k*tmp.charge/denom*(tmp.y-y);
Ez+=k*tmp.charge/denom*(tmp.z-z);
} // end for
f[0] = (this.charge*(Bz*Vy-By*Vz) + this.charge*Ex)/this.mass;
f[1] = (this.charge*(Bx*Vz-Bz*Vx) + this.charge*Ey)/this.mass;
f[2] = (this.charge*(By*Vx-Bx*Vy) + this.charge*Ez)/this.mass;
return f;
}// end force
public void setEditable(boolean bool) {
this.CanEditSettings=bool;
} // end setEditable
public boolean getEditable() {
return this.CanEditSettings;
} // end getEditable
public void setCanMove(boolean bool) {
this.CanMove=bool;
} //end setCanmove
public boolean getCanMove() {
return this.CanMove;
} //end getCanMove
} // end PtCharge
}

Answer 1

You get the ArrayIndexOutOfBoundsException because of this part:
for(int i=0; i<(PartsOnScreen.size()); i++) {
     if(PartsOnScreen.get(i) != null) {
          // color if's
          int tmpcharge = ((PtCharge)PtChargeList.get(i)).charge;
          if(tmpcharge > 0){
               g2.setPaint(Color.blue);
          } else if(tmpcharge < 0) {
               g2.setPaint(Color.red);
          } else {g2.setPaint(Color.gray);} // end color if's
          g2.fill((Ellipse2D)PartsOnScreen.get(i));
     } // end if
} // end forYour for loop goes from 0 to the size of the PartsOnScreen Vector, but you use it to index PtChargeList. That won't work unless you know for sure that PartsOnScreen and PtChargeList are always the same size.
You'll also find that you have a lot of NullPointerExceptions because you don't initialize your local arrays. There are many places where you use double[] f = null;That array doesn't exist yet. You need to allocate storage for it using double[] f = new double[3];The repaint problem happens because you're doing everything on the event dispatch thread. Normally, that thread is used for processing events. When the Simulate MenuItem is pressed, the event dispatch thread runs the actionPerformed code for that menu item, which starts the simulation. The simulation goes into an endless loop, which ties up the event dispatch thread so that it can't process any more events. That's why you can't click on anything or close the window once the simulation has started. The event dispatch thread is stuck calling calculate() over and over.
What your code should do is create a new thread that runs the simulation. That way the event dispatch thread is free to continue processing events.