3-D Space Vector

Question

I wrote the following implementation of a Vector in Java. I was wondering what you folks thought of it.

package space;
public class SpaceVector {
 private final double x;
 private final double y;
 private final double z;
 public SpaceVector(double x, double y, double z){
 this.x = x;
 this.y = y;
 this.z = z;
 }
 public SpaceVector minus(SpaceVector o) {
 return new SpaceVector(x - s.x, y - s.y, z - s.z);
 }
 public double dot(SpaceVector o) {
 return x * o.x + y * o.y + z * o.z;
 }
 public double abs() {
 return Math.sqrt(x * x + y * y + z * z);
 }
 public SpaceVector cross(SpaceVector o) {
 double i, j, k;
 i = y * o.z - z * o.y;
 j = -(x * o.z - z * o.x);
 k = x * o.y - y * o.x;
 return new SpaceVector(i, j, k);
 }
}

Answer 1

Within a mathematical tradition,

• minus is an unary operator, as in

  public minus() {
   return new SpaceVector(-x, -y, -z);
  }
  

• A vector-by-scalar multiplication

  public scale_by(double scalar)
  

  is expected (notice that minus is actually scale_by(-1)).

• Vector addition

  public add(SpaceVector other)
  

  is expected.

• abs is usually called norm.

Answer 2

Personally, I find something like this really hard to read, because it contains so many one letter variables:

 i = y * o.z - z * o.y;
 j = -(x * o.z - z * o.x);
 k = x * o.y - y * o.x;

I would prefer it like this:

 double i = this.y * vector.z - this.z * vector.y;
 double j = this.z * vector.x - this.x * vector.z;
 double k = this.x * vector.y - this.y * vector.x;

You can omit the this if you don't like it, but I think that the vector really helps. Note also that I changed the second line slightly for more readability, and that I declared the variables when assigning values to them, saving a line and increasing readability.

Misc

• minus(SpaceVector o) should be minus(SpaceVector s)
• generally, this is called Vector3d (with the d standing for double), which is a lot more expressive than SpaceVector.