One-liner solution to the TicTacToe kata ;o)

TicTacToe.java

    // Not what I'd call good readable code, but it amuses me ;D

    private boolean playerWon(char player, char[] board) {
        return of(
                // rows
                of(0, 1, 2), of(3, 4, 5), of(6, 7, 8),
                // columns
                of(0, 3, 6), of(1, 4, 7), of(2, 5, 8),
                // diagonals
                of(0, 4, 8),of(2, 4, 6)
        ).anyMatch(combination -> combination.allMatch(position -> board[position] == player));
    }

TicTacToeSimplified.java

    
    // It gets simpler when we replace the concept of board with a list of spots occupied by the player.
    // Yet another example of how design gets simpler by the right choice of data-structure.

    private Stream<List<Integer>> winningCombinations = Stream.of(
            // rows
            asList(0, 1, 2), asList(3, 4, 5), asList(6, 7, 8),
            // columns
            asList(0, 3, 6), asList(1, 4, 7), asList(2, 5, 8),
            // diagonals
            asList(0, 4, 8), asList(2, 4, 6)
    );

    private boolean playerWon(List<Integer> playerSpots) {
        return winningCombinations.anyMatch(playerSpots::containsAll);
    }