public class Vector2D {
	private double x, y;  // we will use cartesian coordinates
	public Vector2D () {
		x = y = 0;
	}
	public Vector2D (double x, double y) {
		this.x = x;
		this.y = y;
	}
	public double getX(){
		return x;
	}
	public double getY(){
		return y;
	}
	public Vector2D plus(Vector2D v) {
     if (v == null) return new Vector2D(x,y);
     return new Vector2D (x+v.getX(), y+v.getY());
	}
	public Vector2D times(double scalar) {
//...
	}
	public Vector2D minus(Vector2D v) {
//...
	}
	public String toString() {
		return "Vector "+x+","+y;
	}
}