How would I move a blank space in a 2d array?

I’m working on a Slider puzzle game and I’m not sure how I would go about moving a “blank” around the array. The puzzle would something like this but randomized. Each method has a prerequisite indicating if it can move a certain direction or not.

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   // Modifies the puzzle by moving the blank up
   // pre: canMoveUp()
   public void up() {
      
   }

   // Modifies the puzzle by moving the blank down
   // pre: canMoveDown()
   public void down() {
      
   }

   // Modifies the puzzle by moving the blank left
   // pre: canMoveLeft()
   public void left() {
      
   }

   // Modifies the puzzle by moving the blank right
   // pre: canMoveRight()
   public void right() {
      
   }

Answer

Here is an example of how you could implement right(), the rest of the methods would follow very similarly. I am assuming, as your comments imply, that the legality of the move has already been verified.

/*
represent the board in a 2-dimensional array with the following coordinate system
  x --->
y
|
/
*/

int x, y = 0; // keeping track of the blank position

int[][] board = ... // initialize the board as needed (sequentially? randomly?), assume -1 represents the blank space

public void right() { // move the blank in the positive x direction
    // get the value currently in the position that the blank must move to, as it will need to be swapped
    int tmp = board[x + 1][y]; 
    board[x + 1][y] = -1; // move the blank here
    board[x][y] = tmp; // complete the swap
    x = x + 1; // the new x position of the blank needs to be updated
}