sudoku using recursive method in java

class Sudoku
{
    private int[][] sudoku;
    private static final int UNASSIGNED = 0;
      
    public Sudoku()
    {
        sudoku = new int[9][9];
    }
      
    public Sudoku(int sudoku[][])
    {
        this.sudoku= sudoku;
    }
      
    //TO-DO Methods
    //private boolean containsInRow(int row,int number){...}
    //private boolean containsInCol(int col,int number){...}
    //private boolean containsInBox(int row, int col,int number){...}
    //private boolean isAllowed(int row, int col,int number){...}
    //public void displaySudoku(){...}
    //public boolean solveSudoku(){...}
}