Vector2D v = new Vector2D(x2, y2);
double dist = new Vector2D(x1, y1).distance(new Vector2D(x2, y2));
v.sub(new Vector2D(x1, y1));
v.norm();
v.mult(this.pfeilSpLaenge);
Vector2D v1 = new Vector2D(x1, y1);
Vector2D v2 = new Vector2D(x2, y2);
v2.sub(v);