public PingPongGame()
 {
     _state = PingPongGameState.NotSet;
     _sets = new List<Set>();
 }
 public void Start()
 {
     _state = PingPongGameState.Started;
 }
 public void End()
 {
     _state = PingPongGameState.Finished;
 }
 public void End()
 {
     _state = PingPongGameState.Finished;
 }
 public void Start()
 {
     _state = PingPongGameState.Started;
 }
 public PingPongGame()
 {
     _state = PingPongGameState.NotSet;
     _sets  = new List <Set>();
 }