TicTacToe(exception thrown wtf)

/**
 * This class implements and evaluates game situations of a TicTacToe game.
 */
public class TicTacToe {

    /**
     * Returns an evaluation for player at the current board state.
     * Arbeitet nach dem Prinzip der Alphabeta-Suche. Works with the principle of Alpha-Beta-Pruning.
     *
     * @param board     current Board object for game situation
     * @param player    player who has a turn
     * @return          rating of game situation from player's point of view
    **/
    public static int alphaBeta(Board board, int player)
    {
        // TODO
        return alphaBeta(board, player, -Integer.MAX_VALUE, Integer.MAX_VALUE, 0);
    }

        //return alphabeta(1, -Integer.MAX_VALUE, Integer.MAX_VALUE);}

    public static int alphaBeta(Board board, int player, int alpha, int beta, int depth) {
        if (board.isGameWon()) {
            return player * (1 + board.free_fields);
        }
        else if (board.free_fields == 0){ //es gibt keine freie felder
            return 0;
        }

        for (Position pos_move : board.validMoves()) {
            board.doMove(pos_move, player);
            int score = - alphaBeta(board, -player, -beta, -alpha, 0);
            board.undoMove(pos_move);
            if (score > alpha) {
                alpha = score;
                if (alpha >= beta) break;
            }
        }
        return alpha;
    }



    /**
     * Vividly prints a rating for each currently possible move out at System.out.
     * (from player's point of view)
     * Uses Alpha-Beta-Pruning to rate the possible moves.
     * formatting: See "Beispiel 1: Bewertung aller Zugmöglichkeiten" (Aufgabenblatt 4).
     *
     * @param board     current Board object for game situation
     * @param player    player who has a turn
    **/

    public static void evaluatePossibleMoves(Board board, int player)
    {
        // TODO
    }

    public static void main(String[] args)
    {
        Board first_board = new Board(3); //leeres Board erstellt
        //Position pos1 = new Position(1, 1);
        //first_board.doMove(pos1, 1); //x gesetzt

        first_board.print();
        System.out.println("Score fuer Spieler 1 : " + TicTacToe.alphaBeta(first_board, 1));
        System.out.println("Score fuer Spieler -1 : " + TicTacToe.alphaBeta(first_board, -1));

    }
}