LeetCode 771宝石与石头(Java)

class Solution {
    public int numJewelsInStones(String J, String S) {
        if(J == null || S== null ) 
            return 0;
        int num = 0;
        for(char s : S.toCharArray()) {
            for(char j : J.toCharArray()) {
                if(s == j) {
                    num ++;
                    break;
                }
            }
        }
        return num;
    }
}