public class Point3d implements Comparable {
  public double x, y, z;
  public Point3d() { 
    this(0.0,0.0,0.0); 
  }
  public Point3d( double _x, double _y, double _z) {
    this.x = _x; this.y = _y; this.z = _z;
  }
  public int compareTo(Object o) {
    Point3d other = (Point3d)o;
    if (x < other.x) {
      return -1;
    }
    else if (x > other.x) {
      return 1;
    }
    else {
      return 0;
    }
  }
}