SudokuChecker

public boolean isValid(char [][]board) {
  for (int i = 0; i < 9; i++) {
    if (!isValid(board, 0, i, 9, 1) || !isValid(board, i, 0, 1, 9)) {
      return false;
    }
  }
  for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
      if (!isValid(board, 3*i, 3*j, 3, 3)) {
        return false;
      }
    }
  }
  return true;
}

private boolean isValid(char [][]board, int y, int x, int h, int w) {
  boolean []used = new boolean[9];
  for (int i = y; i < y + h; i++) {
    for (int j = x; j < x + w; j++) {
      if (board[i][j] != '.') {
        int val = charToInt(board[i][j]);
        if (used[val - 1]) {
          return false;
        } else {
          used[val - 1] = true;
        }
      }
    }
  }
  return true;
}

private int charToInt(char c) {
  return c - '0';
}