public String getBoardSurface() {
        String ret = "";
        for(int y = 0; y < 9; y++) {
            ret += "P" + (y+1);
            for(int x = 0; x < 9; x++) {
                Player player;
                if (attacker.getPieceTypeOnBoardAt(new Point(x, y)) > 0) player = attacker;
                else player = defender;
                Boolean existPiece = player.getPieceTypeOnBoardAt(new Point(x,y)) != Piece.NONE;
                if (player instanceof AheadPlayer && existPiece) ret += "+";
                else if (player instanceof BehindPlayer && existPiece) ret += "-";
                if (!existPiece) ret += " * ";
                else ret += player.getPieceOnBoardAt(new Point(x,y)).getName(true);
            }
            if (y != 8) ret += "\n";
        }
        return ret;
    }