Add Mutlidimensional Array to ArrayList

I want to add a multidimensional Boolean Array to an ArrayList. How do I do that?

Below is an simple example:

public boolean[][] BooleanArray;
ArrayList<Boolean[][]> BooleanArrayList= new ArrayList<Boolean[][]>();

public void AddBooleanArrayToList(){
    BooleanArrayList.add(BooleanArray);
}

However this example does not work. This error will prompt:

The method add(Boolean[][]) in the type ArrayList<Boolean[][]> is not applicable for the arguments (boolean[][])

Answer

The problem here is that you defined the ArrayList to take 2D arrays of the wrapper class Boolean, but you are trying to add a 2D array of the primitive type boolean. Those are not the same type, hence the error. You are able to get away with this when you aren’t storing arrays thanks to a nice little Java feature called auto-boxing, which converts between Boolean and boolean automatically, but auto-boxing isn’t smart enough to work on arrays. The fix is simple; just capitalize the B in “boolean” in the declaration for BooleanArray. It should look like so:

public Boolean[][] BooleanArray;

Alternatively, (not recommended) you could manually box your array when you want to add it to the ArrayList like so:

BooleanArrayList.add(
        IntStream.range(0, BooleanArray.length)
        .mapToObj((i) -> IntStream.range(0, BooleanArray[i].length)
        .mapToObj((j) -> BooleanArray[i][j])
        .toArray(Boolean[]::new))
        .toArray(Boolean[][]::new));