My solution i think its easy to use and implement not sure if its efficient though.

public static List<Integer> rotLeft(List<Integer> a, int d) {
        // Loop from 0 to Number of rotations
        for(int i = 0; i < d ; i++)
        {
                // Get the value at first index of list to temp variable
                int temp = a.get(0);
                // remove the first element
                a.remove(0);
                // add it back to list by default it goes to the end
                a.add(temp);
        }
        return a;
}