Sudoku Recursion Issue (Java)

I'm having an issue with creating a random Sudoku grid. I tried modifying a re开发者_如何学Pythoncursive pattern that I used to solve the puzzle. The puzzle itself is a two dimensional integer array. This is what I have (By the way, the method doesn't only randomize the first row. I had an idea to randomize the first row, then just decided to do the whole grid):

public boolean randomizeFirstRow(int row, int col){
    Random rGen = new Random();

    if(row == 9){
        return true;
    }
    else{
        boolean res;
        for(int ndx = rGen.nextInt() + 1; ndx <= 9;){

            //Input values into the boxes
            sGrid[row][col] = ndx;
            //Then test to see if the value is valid
            if(this.isRowValid(row, sGrid) && this.isColumnValid(col, sGrid) && this.isQuadrantValid(row, col, sGrid)){
                // grid valid, move to the next cell
                if(col + 1 < 9){
                    res = randomizeFirstRow(row, col+1);
                }

                else{
                    res = randomizeFirstRow( row+1, 0);
                }

                //If the value inputed is valid, restart loop
                if(res == true){
                    return true;
                }
            }
        }
    }

    //If no value can be put in, set value to 0 to prevent program counting to 9
    setGridValue(row, col, 0);
    //Return to previous method in stack
    return false;
}

This results in an ArrayIndexOutOfBoundsException with a ridiculously high or low number (+- 100,000). I've tried to see how far it goes into the method, and it never goes beyond this line:

if(this.isRowValid(row, sGrid) && this.isColumnValid(col, sGrid) && this.isQuadrantValid(row, col, sGrid))

I don't understand how the array index goes so high. Can anyone help me out?

 for(int ndx = rGen.nextInt() + 1; ndx <= 9;){

This looks fishy. Random.nextInt() returns a random integer within the integer's full range, not just from 0 to 9.

You'll want this.

public int nextInt(int n) Returns: a pseudorandom, uniformly distributed int value between 0 (inclusive) and n (exclusive).