eyeofmidas.com/htdocs/files/starsystem.pde

System sol;

void setup(){
  size(640, 480);
  sol = new System(width/2, height/2);
}

void draw(){
  sol.update();
  
  background(0,0,0);
  sol.draw();
}


class Planet  {
  //float r3,r,nu,v,hz,h,e;
   
   private float x;
   private float y;
   
   private float xVelocity;
   private float yVelocity;
   
   //private float energy;
   //private float period;
   private float starMass;
   private float r;
   private float r3;
   
  Planet(float inStarMass)  {
    x = 100;
    y = 0;
    xVelocity = 0;
    yVelocity = 10;
    //v = 0;
    r = sqrt((x*x) + (y*y));
    r3 = 1/(r*r*r);
    //nu = 0;
    starMass = inStarMass;
  }
   
  void update()  {
    //hz = (x * yVelocity) - (y * xVelocity);
    //energy = ((v*v)/2) - (starMass/r);
    //e = sqrt(1+ ((2*energy*hz*hz)/(starMass*starMass)));
    //v = sqrt((xVelocity*xVelocity) + (yVelocity*yVelocity));
    //period = (hz * hz) / starMass;
    //nu = acos(((period/r) - 1)/e);
    
    xVelocity -= starMass * x * r3;
    yVelocity -= starMass * y * r3;
    x += xVelocity;
    y += yVelocity;
    
    r = sqrt((x*x) + (y*y));
    r3 = 1/(r*r*r);
    
  }
  
  float getX() {
   return x; 
  }
  
  float getY() {
   return y; 
  }
   
  void draw()  {
    stroke(0,255,0);
    noFill();
    ellipse(x,y,10,10);
  }
}

class Star {
  private float x;
  private float y;
  private float mass;
  private float diameter;
  
  public Star() {
    x = 0;
    y = 0;
    mass = 7000;
    diameter = 70;
  }
  
  public float getMass() {
    return mass;
  }
  
  public void update() {
    
  }
  
  public void draw() {
    stroke(255,255,0);
    noFill();
    ellipse(x,y,diameter,diameter);
  }
}
class System {
  private float x;
  private float y;
  private Star star;
  private Planet[] planets;
  
  public System(float inX, float inY) {
    x = inX;
    y = inY;
   star = new Star();
   planets = new Planet[1];
   for(int i = 0; i < planets.length; i++) {
      planets[i] = new Planet(star.getMass()); 
   }
  }
  
  public void update() {
    star.update();
    for(int i = 0; i < planets.length; i++) {
      planets[i].update();
    }
  }
  
  public void draw() {
    translate(x, y);
    translate(-(planets[0].getX() / 70), -(planets[0].getY() / 70));
    star.draw();
     for(int i = 0; i < planets.length; i++) {
      planets[i].draw();
    }
  }
}