Advanced static typing

Traditional.java

TicTacToe ticTacToe = new TicTacToe();
ticTacToe.move(position);
if(!ticTacToe.isFinished()){
  waitForNextMove(ticTacToe);
}else{
  handleGameResult(ticTacToe);
}

Types.java

EmptyTicTacToe ticTacToe = new EmptyTicTacToe();
ticTacToe.move(position, new OnMoveResult() {
  
  public void onGameRunning(RunningTicTacToe ticTacToe) {
    waitForNextMove(ticTacToe);
  }

  public void onGameEnded(FinishedTicTacToe ticTacToe) {
    handleGameResult(ticTacToe);
  }

});