Vektor2D v = new Vektor2D(x2, y2);
double dist = new Vektor2D(x1, y1).distanz(new Vektor2D(x2, y2));
v.sub(new Vektor2D(x1, y1));
v.normal();
v.mult(this.pfeilSpLaenge);
Vektor2D v1 = new Vektor2D(x1, y1);
Vektor2D v2 = new Vektor2D(x2, y2);
v2.sub(v);