Question

This is the relevant code I think

class Sudoku {
    int[][] grid;     

    void generateSudokuFromInput()
    {

      grid = new int[][]   <--- java.lang.NullPointerException at Sudoku.generateSudokuFromInput(Sudoku.java:309)
      {
         (...)
      }
    }

    void solveIt() {

      generateSudokuFromInput(); 

    }

}

Keep getting NullPointer error

Answer 1

As an alternative to declaring the array size later (as described in other answers), you can also just initialize your array when declaring it:

class Sudoku {
    int[][] grid = {
        {0, 0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0, 0}
    };

    void generateSudokuFromInput() {
        // just set the values on grid, e.g. grid[0][0] = 9
    }

    void solveIt() {
        generateSudokuFromInput();
    }
}