Jewels And Stones

//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".

class JewelsAndStones {
    public int numJewelsInStones(String J, String S) {
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        for(char c: J.toCharArray()) {
            map.put(c, 1);
        }
       
        int numberOfJewels = 0;
        for(char c: S.toCharArray()) {
            if(map.containsKey(c)) {
                numberOfJewels++;
            }
        }
       
        return numberOfJewels;
    }
}