Let me be brief. I am creating a n-body simulation for a school-project. I've encountered a problem: I get the error IndexOutOfBoundsException only sometimes when I run the simulation. There does not seem to be any correlation between when I get the error. I am assuming I am destroying the bodies (via the collision detection method) too quickly for it to register, and it tries to access an index that no longer exists. I thought
if(bodies.get(i)!=null&&bodies.get(n)!= null)
in the update method would fix it, but it did not. Could someone take a look at the code and tell me what might be causing the error? To recreate the error: Simply press 'o' in the simulation, or randomly spawn massive bodies with 'm' until it occurs. Please keep in mind that I am only in high school, and I have not got a lot of programming experience.
MAIN:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Main extends JPanel implements Runnable, KeyListener{
public static int width = 1400;
public static int height = (width/16) * 9;
public String title = "Orbital Mechanics Simulator -";
public Dimension dim = new Dimension(width, height);
public boolean running;
Color bgColor = new Color(0x000000);
public static long timeScale = (long) Math.pow(10,7.5); //how many simulation-seconds one IRL-second represents.
public static long distanceScale = ((Physics.astUnit*10L) / width); //how many meters does one pixel represent
ArrayList<Body> bodies = new ArrayList<Body>();
long initFpsTime;
long secondFpsTime;
long nowTime;
long lastTime;
long timeElapsed;
float deltaTime;
int fps = 200;
public Main(){
this.setPreferredSize(dim);
this.setBackground(bgColor);
this.start();
}
public void start(){
running = true;
Thread program = new Thread(this, "update");
program.start();
}
public void run(){
lastTime = System.nanoTime();
while(running){
nowTime = System.nanoTime();
deltaTime = nowTime - lastTime;
update(deltaTime);
initFpsTime = System.currentTimeMillis();
if((initFpsTime - secondFpsTime) > Math.pow(10,3) / fps){
render();
secondFpsTime = System.currentTimeMillis();
}
}
}
public void update(float deltaTime){
for(int i=0; i<bodies.size();i++){
resetForces();
bodies.get(i).update((float)(deltaTime / Math.pow(10,9))*timeScale);
lastTime = System.nanoTime();
//sets the forces for all bodies
for(int n=0; n<bodies.size();n++){
if(bodies.get(i)!=bodies.get(n)){
if(bodies.get(i)!=null&&bodies.get(n)!= null)
bodies.get(i).setForce(Physics.getFx(bodies.get(i), bodies.get(n)), Physics.getFy(bodies.get(i), bodies.get(n)));
//collision detection
if(Physics.getDistanceBetween(bodies.get(i), bodies.get(n)) < (bodies.get(i).radius + bodies.get(n).radius)*distanceScale){
collision(bodies.get(i),bodies.get(n));
}
}
}
}
}
//DIFFERENT SYSTEMS
public void solarSystem(){
Body sun;
Body earth;
Body mars;
sun = new Body("Sun", Physics.massSun, 20, 0,0, new Color(0xffff00), (float)0, (float)0);
earth = new Body("earth", Physics.massEarth, 10, Physics.astUnit/distanceScale,0, new Color(0x0000ff), (float)0, (float)0);
mars = new Body("Mars", Physics.massEarth, 10, (long)(1.5*Physics.astUnit/distanceScale) ,0, new Color(0x00ff00), (float)0, (float)0);
earth.setVelocity(0,(float)Physics.getInitVy((long)Physics.getDistanceBetween(earth, sun), sun));
mars.setVelocity(0,(float)Physics.getInitVy((long)Physics.getDistanceBetween(mars, sun), sun));
bodies.add(sun);
bodies.add(earth);
bodies.add(mars);
}
public void twoBodies(){
bodies.add(new Body("Sun", Physics.massSun, 20, 0,0, new Color(0xffff00), (float)0, (float)0));
bodies.add(new Body("earth", Physics.massEarth, 10, Physics.astUnit/distanceScale,0, new Color(0x0000ff), (float)0, (float)0));
bodies.add(new Body("Mars", Physics.massMars, 10, (long)(1.5*Physics.astUnit/(distanceScale)),0 ,new Color(0x00ff00), (float)0, (float)0));
//earth.setVelocity(0,(float)Physics.getInitVy((long)Physics.getDistanceBetween(earth, sun), sun));
//mars.setVelocity(0,(float)Physics.getInitVy((long)Physics.getDistanceBetween(mars, sun), sun));
}
public void createRandomBody(){
bodies.add(new Body("randomBody",Physics.massSun,10, Physics.randomXPos(), Physics.randomYPos(), Physics.randomColor(),(float)0,(float)0));
}
public void createMassiveBody(){
bodies.add(new Body("Sun",Physics.massSun,10, Physics.randomXPos(), Physics.randomYPos(), Physics.randomColor(),(float)0,(float)0));
}
public void createSmallBody(){
bodies.add(new Body("Earth",Physics.massEarth,10, 0, 0, Physics.randomColor(), (float)0, (float)0));
}
public void createSystem(){
for(int i=0; i<20;i++){
for(int n=0; n<20;n++){
bodies.add(new Body("Random", Physics.massSun, 4, -width/2 + n*20 , height/2 - i*20 , Color.WHITE, (float)0, (float)0 ));
}
}
}
public void resetForces(){
if(bodies.get(0) != null);
for(int i=0;i<bodies.size();i++){
if(i<=0 && i < bodies.size()){
bodies.get(i).resetForce();
}
}
}
public void collision(Body a, Body b){
Body newBody = new Body("newBody", a.mass+b.mass, 20, (a.xPos+b.xPos)/2, (a.yPos+b.yPos)/2, Physics.randomColor(), (a.mass*a.vx + b.mass*b.vx)/(a.mass+b.mass), (a.mass*a.vy+b.mass*b.vy)/(a.mass+b.mass));
bodies.remove(a);
bodies.remove(b);
bodies.add(newBody);
}
public void render(){
repaint();
}
public void keyPressed(KeyEvent event) {
switch(event.getKeyChar()){
case 'r': createRandomBody();
break;
case 'f': twoBodies();
break;
case 'm':
createMassiveBody();
break;
case 'z':
createSmallBody();
break;
case 'o':
createSystem();
break;
case 's':
solarSystem();
break;
}
}
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); //quick vs quality - preferring quality
for(int i=0;i<bodies.size();i++){
bodies.get(i).displayPlanet(g2d);
}
}
public static void gui(){
Main main = new Main();
JFrame frame = new JFrame();
frame.setResizable(false);
frame.setTitle(main.title);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(main);
frame.addKeyListener(main);
frame.pack();
frame.setVisible(true);
}
public static void main(String args[]){
SwingUtilities.invokeLater(new Runnable(){ //Event dispatching thread
public void run(){
gui();
}
});
}
@Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
@Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
}
}
BODY
import java.awt.Color;
import java.awt.Graphics;
public class Body {
public static int xOrigo = Main.width / 2;
public static int yOrigo = ((Main.width * 9) / 16) / 2;
public static int numOfBodies; // how many bodies the program contains.
public static float distanceScale = Main.distanceScale;
public String name;
public float mass, fx, fy, accX, accY, vx, vy, initVx, initVy, deltaX, deltaY;
public long xDisplay, yDisplay;
public long xPos, yPos;
public int radius;
public Color color;
public Body(String name, float mass, int radius, long xPos, long yPos, Color color, float initVx, float initVy){
this.name = name;
this.mass = mass;
this.radius = radius;
this.color = color;
numOfBodies++;
setX(xPos);
setY(yPos);
setVelocity(initVx, initVy);
}
public void update(float deltaTime){
this.deltaX += this.vx * deltaTime;
if(this.deltaX >= distanceScale){
this.incX();
deltaX = 0;
}else if(this.deltaX <= -distanceScale){
this.decX();
deltaX = 0;
}
this.deltaY += this.vy * deltaTime;
if(this.deltaY >= distanceScale){
this.incY();
deltaY = 0;
}else if(this.deltaY <= -distanceScale){
this.decY();
deltaY = 0;
}
this.vx += (this.accX * deltaTime);
this.vy += (this.accY * deltaTime);
}
public void setX(long xPos){
this.xPos = xPos;
this.xDisplay = xOrigo + xPos - radius;
}
public void setY(long yPos){
this.yPos = yPos;
this.yDisplay = yOrigo - yPos - radius;
}
public void incX(){
this.xPos++;
this.xDisplay = xOrigo + xPos - radius;
}
public void decX(){
this.xPos--;
this.xDisplay = xOrigo + xPos - radius;
}
public void incY(){
this.yPos++;
this.yDisplay = yOrigo - yPos - radius;
}
public void decY(){
this.yPos--;
this.yDisplay = yOrigo - yPos - radius;
}
public void setForce(float fx, float fy){
this.fx += fx;
this.accX = fx / this.mass;
this.fy += fy;
this.accY = fy / this.mass;
}
public void setVelocity(float vx, float vy){
this.vx += vx;
this.vy += vy;
}
public void displayPlanet(Graphics g){
g.setColor(this.color);
g.fillOval((int )this.xDisplay, (int)this.yDisplay, this.radius*2, this.radius*2); //temporary fix
}
public long getXPos(){
return this.xPos;
}
public long getYPos(){
return this.yPos;
}
public void resetForce(){
this.fx = 0;
this.fy = 0;
}
}
PHYSICS:
import java.awt.Color;
import java.util.Random;
public class Physics {
public static Random rand = new Random();
public static final double G = 6.67384*(Math.pow(10, -11));
public static long astUnit = 149597871000L; //L IS TO INDICATE IT'S A LONG VALUE, otherwise neg value
public static float massEarth = (float)(5.97219*Math.pow(10,24));
public static float massSun = (float)(1.9891*Math.pow(10,30));
public stati
