Reassigning array values in array of primitives does not change array

Question

I try to set the values of a 2D boolean array with 2 loops like this:

 boolean[][] frame = new boolean[10][4];
    for (boolean[] column : frame)
        for (boolean b : column)
            b = true;

But that doesnt seem to work, all booleans remain false, why?

Answer 1

You cannot assign new values to objects in an array, because the original object will not be changed. Following code will do the trick.

boolean[][] frame = new boolean[10][4];
for (boolean[] column : frame)
    for (int i = 0; i < column.length; i++)
        column[i] = true;

A bit more explanation:

The array contains elements which point to booleans. When you assign the value of one of the elements of the array to a variable called b (for (boolean b : column)), the variable b points to the same object the element in the array points to. Next, you point the variable b to true. Now, b will be true. However, the element in the array still points to the same object.

I hope this is clear now. An image would make it more understandable...