static void printSolution(SudokuBoard board) {

    SudokuBoard resultBoard = findSolution(board);

    if(resultBoard != null) {
        resultBoard.print();
    }
}

static SudokuBoard findSolution(SudokuBoard board) {

    if (board.isSolved()) {
        return board;

    } else {

        int freiesNaechstesFeld = getNextFreeIndex(board);

        if (freiesNaechstesFeld != -1) {

            int[] kandidaten = board.getCandidates(freiesNaechstesFeld);

            for (int i = 0; i < kandidaten.length; i++) {

                SudokuBoard newBoard = board.set(freiesNaechstesFeld,
                        kandidaten[i]);

                return findSolution(newBoard);
            }
        }

        return null;
    }
}