Removed preCalc

src/Body.java

@@ -4,7 +4,7 @@ import codedraw.CodeDraw;
  * This class represents celestial bodies like stars, planets, asteroids, etc...
  */
 public class Body {
-    private final double mass;
+    private double mass;
     private Vector massCenter; // position of the mass center.
     private Vector currentMovement;
 
@@ -83,6 +83,12 @@ public class Body {
         return massCenter;
     }
 
+    public void update(Body b) {
+        double combinedMass = this.mass + b.mass;
+        this.massCenter = this.massCenter.times(this.mass / combinedMass).plus(b.massCenter.times(b.mass / combinedMass));
+        this.mass = combinedMass;
+    }
+
     public boolean collidesWith(Body body) {
         return this.distanceTo(body) < this.radius() + body.radius();
     }

src/Octree.java

@@ -38,7 +38,6 @@ public class Octree {
 
     public void applyForces(Body[] bodies, double t) {
         if (root == null) return;
-        root.preCalc();
         Vector[] forces = new Vector[bodies.length];
         for (int i = 0; i < bodies.length; i++) {
             forces[i] = root.getForcesOnBody(bodies[i], t);
@@ -67,8 +66,6 @@ abstract class OctreeItem {
 
     abstract protected OctreeNode add(Body body);
 
-    abstract protected void preCalc();
-
     abstract protected Vector getForcesOnBody(Body body, double t);
 
     abstract protected void draw(CodeDraw cd);
@@ -90,6 +87,11 @@ class OctreeNode extends OctreeItem {
     protected OctreeNode add(Body body) {
         int num = getOctantNum(body.massCenter());
         if (num < 0) return this;
+        if (this.pseudoBody == null) {
+            this.pseudoBody = new Body(body);
+        } else {
+            this.pseudoBody.update(body);
+        }
         OctreeItem oct = children[num];
         if (oct == null) {
             children[num] = new OctreeLeaf(getOctantCenter(num), size / 2, body);
@@ -99,22 +101,6 @@ class OctreeNode extends OctreeItem {
         return this;
     }
 
-    @Override
-    protected void preCalc() {
-        double mass = 0;
-        for (OctreeItem oct : children) {
-            if (oct == null) continue;
-            oct.preCalc();
-            mass += oct.pseudoBody.mass();
-        }
-        Vector massCenter = new Vector();
-        for (OctreeItem oct : children) {
-            if (oct == null) continue;
-            massCenter.add(oct.pseudoBody.massCenter().times(oct.pseudoBody.mass() / mass));
-        }
-        this.pseudoBody = new Body(mass, massCenter);
-    }
-
     @Override
     protected Vector getForcesOnBody(Body body, double t) {
         double r = pseudoBody.massCenter().distanceTo(body.massCenter());
@@ -171,6 +157,7 @@ class OctreeLeaf extends OctreeItem {
     public OctreeLeaf(Vector center, double size, Body body) {
         super(center, size);
         this.body = body;
+        this.pseudoBody = new Body(this.body);
     }
 
     @Override
@@ -178,11 +165,6 @@ class OctreeLeaf extends OctreeItem {
         return new OctreeNode(this.center, this.size).add(this.body).add(body);
     }
 
-    @Override
-    protected void preCalc() {
-        this.pseudoBody = new Body(this.body);
-    }
-
     @Override
     protected Vector getForcesOnBody(Body body, double t) {
         return body.gravitationalForce(pseudoBody);

src/Simulation.java

@@ -22,7 +22,7 @@ public class Simulation {
 
     // set some system parameters
     public static final double SECTION_SIZE = 2 * AU; // the size of the square region in space
-    public static final int NUMBER_OF_BODIES = 22;
+    public static final int NUMBER_OF_BODIES = 220;
     public static final double OVERALL_SYSTEM_MASS = 20 * SUN_MASS; // kilograms
 
     public static void main(String[] args) {
@@ -68,7 +68,7 @@ public class Simulation {
             }
             octree.applyForces(bodies, 1);
 
-            if ((seconds % 3600) == 0) {
+            if ((seconds % 60) == 0) {
                 cd.clear(Color.BLACK);
                 for (Body body : bodies) {
                     body.draw(cd);