public class Point3D extends Point {
  /* DON'T DO THIS. We
  // already inherited an x and a y
  // this is creating new ones
  // (and a whole lot of confusion)
  // 
  // int x;
  // int y;
  int z;

  public Point3D(int x, int y, int z) {
    super(x, y);
    this.z = z;
  }
}