Error sorting vertices using a maximising heap

Posted on 2004-04-11
Last Modified: 2013-11-23
      I'm attempting to sort some 3D shapes by inserting their vertices into a max-heap and then removing the maximum value until the vertices are in descending order.  But so far i've encountered three errors. Please take a look at my code and the error messages and tell me what you think.

public class OcclusionPipeline extends Mesh implements RenderPipeline{
    Point3D[] pts;
    private int size;
    public int capacity(){return(pts.length);}
    public int size(){return(size);}
    public OcclusionPipeline(Point3D[] pts){
    pts = new Point3D[2];
    size = 0;
   public OcclusionPipeline(int initialCapacity)
         pts = new Point3D[initialCapacity];
         size = 0;
   private int parent(int i)
            return ((i - 1) / 2);

      private int left(int i)
            return (i * 2 + 1);

      private int right(int i)
            return (i * 2 + 2);

      private void swap(int i, int j)
            Point3D temp;

            temp   = pts[i];
            pts[i] = pts[j];
            pts[j] = temp;

      private void heapify(int i)
            int leftChild  = left(i);
            int rightChild = right(i);
            int greatest   = i;

            if(leftChild < size() && pts[leftChild] > pts[i])
                    greatest = leftChild;

            if (rightChild < size() && pts[rightChild] > pts[greatest])
                  greatest = rightChild;

            if (greatest != i) {
                  swap(i, greatest);

  public void deleteMax()
            if (size() > 0) {
                  pts[0] = pts[--size];

                  if (size() * 2 < capacity() && size() > 2) {
                        Point3D[] tmp = new Point3D[size()];

                        for (int i = 0; i < tmp.length; i++)
                              tmp[i] = pts[i];

                        pts = tmp;
            else {
                  System.err.println("deleteMax failed");

      public void insert(Point3D v_item)
            int current;

            if (size == capacity()) {
                  Point3D[] tmp = new Point3D[2 * pts.length];

                  for (int i = 0; i < pts.length; i++)
                        tmp[i] = pts[i];

                  pts = tmp;

            current = size++;

            while (current != 0 && pts[parent(current)] < v_item) {
                  pts[current] = pts[parent(current)];

                  current = parent(current);

            pts[current] = v_item;

      public Point3D max()
            if (size > 0)
                  return pts[0];

            System.err.println("max failed");

The javac compiler gives the following error messages:

Operator > cannot be applied to g3d.geom.Point3D, g3d.geom.Point3D
            if(leftChild < size() && pts[leftChild] > pts[i])

Operator > cannot be applied to g3d.geom.Point3D, g3d.geom.Point3D
            if (rightChild < size() && pts[rightChild] > pts[greatest])

Operator < cannot be applied to g3d.geom.Point3D, g3d.geom.Point3D
            while (current != 0 && pts[parent(current)] < v_item)
Question by:capbry
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LVL 92

Assisted Solution

objects earned 150 total points
ID: 10803793
ypou cannot use the < and > operators with your Point3D instances.
You need to instead compare the x, y, z values assciated with that object.
LVL 30

Accepted Solution

Mayank S earned 350 total points
ID: 10803898
I'm assuming that Point3D is your own class? You must be having some getX (), getY (), getZ () methods (or some ways to access the co-ordinates)? Elaborating a little more on what objects said, you should use:

if ( rightChild.getX () < size () && .... so on
LVL 30

Expert Comment

by:Mayank S
ID: 10839220
Glad to help ;-)

BTW, why a C :-( you could've asked for more help if you wanted clarification.

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