You must initialize the final fields, but you just initialized local variables in the constructor.
Change
String _name = name;
double _x = x;
double _y = y;
double _energy = energy;
double _heading = heading;
double _velocity = velocity;
to
this._name = name;
this._x = x;
this._y = y;
this._energy = energy;
this._heading = heading;
this._velocity = velocity;