Two int arrays common element count

public class AlgorithmProblem{

    // Given two arrays (elements are sorted and distinct),
    // find the number of elements in common.

     public static void main(String[] args){
        int[] array1 = {1, 2, 3, 5, 8, 13, 21, 34, 55};
        int[] array2 = {2, 8, 10, 11, 12, 14, 15, 16, 17, 55};

        int result = commonElementCount(array1, array2);
        System.out.println(result);
    }

    private static int commonElementCount(int[] a, int[] b){
        if(a == null || b == null)
            throw new IllegalArgumentException();
        int i = 0;
        int j = 0;
        int common = 0;

        while(i < a.length && j < b.length){
            if(a[i] == b[j]){
                common++;
                i++;
                j++;
            } else if(a[i] > b[j]){
                j++;
            } else {
                i++;
            }
        }

        return common;
    }
}