code: public double distance(Vector2D vector2d) {
  		double a = vector2d.x - x;
  		double b = vector2d.y - y;
  		return Math.sqrt(a * a + b * b);
  	}
docs: Calculate the distance between 2 vector by using Pythagoras' formula.
  
  @param vector2d
  The other vector.
  @returns The distance between these 2 vectors as a Double.