Java Recursion Issue: Minesweeper

Question

I just picked up Java a few days ago, and started coding a Minesweeper game. The problem is, when I try to cascade the surrounding blocks and reveal blocks, either blank or with numbers depending on the amount of adjacent bombs, my recursion fails and gives me a stack over flow error. My code is as follows:

public void revealCell(int row, int col) 
{
  if(mAnswerBoard.get (row, col).equals ("1")||mAnswerBoard.get (row, col).equals("2")||
  mAnswerBoard.get (row, col).equals("3")||mAnswerBoard.get (row, col).equals("4")||
  mAnswerBoard.get (row, col).equals("5"))
  {
      mMinesweeperBoard.set (row, col, mAnswerBoard.get (row, col));
      return;
  }

  else if(mAnswerBoard.get (row, col).equals("0"))
  {
      mMinesweeperBoard.set (row, col, " ");
      for(int i = row - 1; i <= row + 1; i++)
      {
        if (i == -1)
        {
          i = 0;
       }
      for(int j = col - 1; j <= col + 1; j++)
      {
        if (j == -1)
        {
          j = 0;
        }
        if (mAnswerBoard.get (i, j).equals ("0") == false)
            {
              mMinesweeperBoard.set (i, j, mAnswerBoard.get (i, j));
            }
            else if (mAnswerBoard.get (i, j).equals (("0")))
            {
             if (mMinesweeperBoard.get (j, i).equals ("."))
             {
                mMinesweeperBoard.set(i, j, " "); 
               revealCell(i, j);
             }
           }
          }
      }
  }
}

I have been staring at this for hours, and I really can't grasp my head around why it doesn't stop looping. My initial gameboard holds "." in not revealed spots, and if 0, the board will hold a whitespace. I try to check if the answer key holds a 0 in the spot, and if it does and if the actual board still holds a"." in the spot, I can set a whitespace. For some reason, revealCell gets called over and over again, and I really can't figure it out. Am I doing something completely wrong?

Side note: I have to set i and j to 0 if they are -1 because my code allows the user to enter in 0,0 as a valid coordinate.

Thank you for the help, and I am sorry if the answer is right in front of my face...

Do you need a recursive solution? I think your iterative approach is probably easier here. — Elliott Frisch
– Elliott Frisch, Commented Jan 10, 2014 at 5:51
I do not necessarily need a recursive solution, but I guess I thought a recursive solution would be more appealing to the eye. In my case though, the code already has lost the appeal. Would an iterative approach be easier? — user3040968
– user3040968, Commented Jan 10, 2014 at 5:53
Are you using a debugger? Recursion problems are often easily troubleshot with some strategic breakpoints. — DeathByTensors
– DeathByTensors, Commented Jan 10, 2014 at 5:54
You're checking if the recursion goes off the left and top of the board, but not the bottom or right sides. That may be an issue later. — user2357112
– user2357112, Commented Jan 10, 2014 at 5:57
@DrewBuckley I have been trying to debug for a while. I'll keep going and see if I can pinpoint the issue. A break may be needed...maybe I've been looking past it all along. — user3040968
– user3040968, Commented Jan 10, 2014 at 6:09

user2357112 · Accepted Answer · 2014-01-10 05:54:36Z

1

             if (mMinesweeperBoard.get (j, i).equals ("."))

You switched i and j here, so you're testing the wrong cell. Switch them back and see if that fixes it.

answered Jan 10, 2014 at 5:54

user2357112

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4 Comments

user3040968 Over a year ago

That gave me an array index out of bounds exception of 9? Not sure how that happened exactly...

user2357112 Over a year ago

That's probably the other issue I mentioned in a comment. You're running off the sides of the array, since you only have half the necessary bounds-checking.

user3040968 Over a year ago

So now i'll have to add checks alongside the checks for the -1?

user2357112 Over a year ago

Yup. And because that's too short to be a comment, double yup.

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