/** Star constructor. */
public Star(double star_pos_x, double star_pos_y) {
my_physics = new PhysicsClass();
// my_animation = new Animation();
my_physics.mass(STAR_MASS);
my_physics.position_x(star_pos_x);
my_physics.position_y(star_pos_y);
}
// @ ensures 0 <= \result;
public /*@ pure @*/ double mass() {
return my_physics.mass();
}