Why does this recursive method for a sudoku-solver keep on spinning?

In a school assignment we're supposed to make a soduko-solver. I have a recursive method that's supposed to help me solve the soduko-puzzles. It goes like this:

public void setNumber() {

if (getNext() == null) {

    for (int i = 1; i < 10; i++) {
    if (acceptValue(i)) {
        value = i;
    }
    }
    board.stopRec();
    return; 

} else { 


    if(predefined()) { // if the square allready has a number
    getNext().setNumber();
    } else { // find value for undefined square

    for (int i = 1; i < 10; i++) {
        if (acceptValue(i)) {
        value = i // Does the Row class take notice of this?
        getNext().setNumber();
        }
    }
    /* no value was assigned */
    value = -1;

    }

}

}

The Board class has a method initGrid, that creates all the Squares and link them together using a nextSquare reference

class Board {

[...]

public void initGrid(int nSquaresBoxRowCol, int nRowsBox, int nColsBox, int[][] values) {

[...]

/* Create the rows, columns and squares */
Square prev = null;
for (int row = 1; row <= nRowsBoard; row++) {

    //Row r = new Row(row, squares[row-1]);
    Row r = new Row(row);
    rows[row-1] = r;

    for (int col = 1; col <= nColsBoard; col++) {
    if (row == 1) {
        Column c = new Column(col);
    }

    Square current = new Square(row, col, Math.ceil((float)row / (float)nRowsBox), Math.ceil((float)col / (float)nColsBox), values[row-1][col-1], r, this);

    if (!((row-1) == 0 && (col-1) == 0)) {
        p开发者_运维知识库rev.nextSquare = current;
    }

    prev = current;
    squares[row-1][col-1] = current;

    r.addSquare(current);

    /* Fill the boxes with squares */
    boxes[(int)(Math.ceil((float)row / (float)nRowsBox)) - 1][(int)(Math.ceil((float)col / (float)nColsBox)) - 1].addSquare(squares[row-1][col-1]);
    nSquares++;

    }

} // END for (int row ...

Objects of the Row class hopefully hold the square objects added to them in the initGrid-method in the Board class.

class Row {
int id;

Square[] squares;
ArrayList<Square> squareList;

Row(int id) {
this.id = id; // not currently used for anything
squareList = new ArrayList<Square>();
}

boolean checkValue(int val) {
System.out.println("Checking values for row " + id);    
Iterator<Square> iter  = squareList.iterator();
while(iter.hasNext()) {
    System.out.println("Value (boolean checkValue() in Row): " + iter.next().value);
    if (iter.next().value == val) {
    System.out.println("returned false");
    return false;
    }
}
return true;

}

public void addSquare(Square s) {
squareList.add(s);
System.out.println("class Row, method addSquare: Square with value " + s.value + " added to row.");
}

}

---

About the semi-recursive method

The method is inside class Square, all the squares are assembled in a two-dimensional array. The method is suppose to call itself for every square on the sudoku board. All the squares have a Square nextSquare pointer pointing at the next square in squares[][]. getNext() returns nextSquare.

acceptValue(i) checks the Squares' Row to see if there's a Square-object there with the value of i, it returns true if there isn't (Row has a square[], with its squares, assigned to it from Board)

I really thought this would do the trick, but the recurrsion just keep on spinning.

The only thing I can think of is that maybe the squares in the Row-object don't get the value-update going on in the recursion, and that this might cause the recursive method to go on forever. But I still don't see why that would make any sense, it should just give me wrong values according to the sudoku rules.

Please advise if I should include any more code.

Any suggestions is much appreciated. Thanks.

---

Well for one thing, if all of your other code works as expected and acceptValue(i) will really choose correctly everytime, then you would want a return after your getNext().setNumber();

Something like

for(i=1;i<10;i++){
    if(acceptValue(i)){
        value = i;
        getNext().setNumber();
        return;
    }
}

Otherwise if your code chose 2 as the value when the setNumber() returns it will try 3, 4, 5... and so on.