First Bad Version

You’re given strings J representing the types of stones that are jewels, and S representing the stones you have. Each character in S is a type of stone you have. You want to know how many of the stones you have are also jewels.

The letters in J are guaranteed distinct, and all characters in J and S are letters. Letters are case sensitive, so “a” is considered a different type of stone from “A”.

Example 1:

Input: J = "aA", S = "aAAbbbb"
Output: 3

Example 2:

Input: J = "z", S = "ZZ"
Output: 0

Note:

    S and J will consist of letters and have length at most 50.
    The characters in J are distinct.

Solution:

class Solution {
    public int numJewelsInStones(String J, String S) {
        final Set<Character> jewels = new HashSet<>();
        for (int i = 0; i < J.length(); i++) {
            jewels.add(Character.valueOf(J.charAt(i)));
        }
        int count = 0;
        for (int i = 0; i < S.length(); i++) {
            if (jewels.contains(Character.valueOf(S.charAt(i)))) {
                count++;
            }
        }
        return count;
    }
}