question: public PlaLineInt translate_by ( PlaVectorInt p_vector ) { if ( p_vector . equals ( PlaVectorInt . ZERO ) ) return this ; PlaPointInt new_a = point_a . translate_by ( p_vector ) ; PlaPointInt new_b = point_b . translate_by ( p_vector ) ; return new PlaLineInt ( new_a , new_b ) ; }
target:  translates the line by p_vector