/**
* Vector2d.java
* Represents some operations on 2-D vectors for geometry and basic
* physics computations.
*
*/
class Vector2d {
   private float x = 0, y = 0;

   /**
    * Default Constructor.
    *
    */
   public Vector2d() { x = 0; y = 0; }
 
   /**
    * Parameterized Constructor.  Sets the member variables to
    * the values passed in.
    * @param xv The desired value of x
    * @param yv The desired value of y
    */
   public Vector2d(float xv, float yv) { x = xv; y = yv; }
   public Vector2d(double xv, double yv) { x = (float)xv; y = (float)yv;
}

   // Accessor/Settor functions.
   public void X(float xv) { x = xv; }
   public void Y(float yv) { y = yv; }
   public float X() { return x; }
   public float Y() { return x; }
 
   /**
    * Add two vectors
    * @param rhs the right hand side vector to be added
    * @return a new vector, the sum of this + rhs.
    */
   public Vector2d add(Vector2d rhs) {
    return new Vector2d(x + rhs.x, y + rhs.y);
   }
 
   /**
    * Subtract two vectors.
    * @param rhs the right hand side vector
    * @return a new vector, this - rhs
    */
   public Vector2d sub(Vector2d rhs) {
    return new Vector2d(x - rhs.x, y - rhs.y);
   }

   /**
    * Negate a vector
    * @return A new vector equal to -this
    */
   public Vector2d neg() {
    return new Vector2d(-x, -y);
   }

   /**
    * Multiply a vector by a constant.
    * @param d the constant by which the vector will be scaled.
    * @return a new vector equal to d*this
    */
   public Vector2d scale(float d) {
    return new Vector2d(x * d, y * d);
   }

   /**
    * Determine the magnitude of a vector.
    * @return Return the magnitude of this
    */
   public float mag() {
    return (float) Math.sqrt(x*x + y*y);
   }

   /**
    * Equality test for vectors.
    * @param rhs The vector to compare to
    * @return true if the vectors have the same components, false
othewise.
    */
   public boolean equals(Vector2d rhs) {
    return (x == rhs.x) && (y == rhs.y);
   }
}