I'm building a simple Sudoku game in Java which is based on a matrix (an array[9][9]) and I need to validate my board state according to these rules:

• all rows have 1-9 digits
• all columns have 1-9 digits.
• each 3x3 grid has 1-9 digits.

This function should be efficient as possible for example if first case is not valid I believe there's no need to check other cases and so on (correct me if I'm wrong).

When I tried doing this I had a conflict. Should I do one large for loop and inside check columns and row (in two other loops) or should I do each test separately and verify every case by it's own?

(Please don't suggest too advanced solutions with other class/object helpers.)

This is what I thought about:

Main validating function (which I want pretty clean):

public boolean testBoard() {

        boolean isBoardValid = false;

        if (validRows())
        {
            if (validColumns())
            {
                if (validCube())
                {
                    isBoardValid = true;
                }
            }
        }
        return isBoardValid;
}

Different methods to do the specific test such as:

private boolean validRows() {
        int rowsDigitsCount = 0;

        for (int num = 1; num <= 9; num++) {
            boolean foundDigit = false;

            for (int row = 0; (row < board.length) && (!foundDigit); row++) {
                for (int col = 0; col < board[row].length; col++) {
                    if (board[row][col] == num) {
                        rowsDigitsCount++;
                        foundDigit = true;
                        break;
                    }
                }
            }
        }

        return rowsDigitsCount == 9 ? true : false;
    }

I don't know if I should keep doing tests separately because it looks like I'm duplicating my code.