I found the below solution on youtube. In my opinion, this is the easiest one to understand and honestly much more elegant than what is given here.

public static void sortColors_3Pointers(int[] nums) {

    int start = 0;
    int mid = 0;
    int end = nums.length - 1;

    while (mid <= end) {

        switch (nums[mid]) {
            case 0:
                // Swap with start index
                swap(nums, start, mid);
                mid++;
                start++;
                break;

            case 1:
                mid++;// do nothing
                break;

            case 2:
                // Swap with end index
                swap(nums, mid, end);
                end--;
                break;
        }
    }

}