Checking Happy number

HappyNumber.java

import java.util.HashSet;
import java.util.Set;

/**
 * Happy number (https://en.wikipedia.org/wiki/Happy_number) : A happy number is a number defined by the following process: 
 * Starting with any positive integer, replace the number by the sum of the squares of its digits, 
 * and repeat the process until the number either equals 1 (where it will stay), 
 * or it loops endlessly in a cycle which does not include 1. 
 * Those numbers for which this process ends in 1 are happy numbers, 
 * while those that do not end in 1 are unhappy numbers (or sad numbers).
 * Created by Daehee Han(@daniel_booknara) on 4/21/16.
 */
public class HappyNumber {
    public static void main(String[] args) {
        int value = 31;
        if (isHappyNumber(value))
            System.out.println("Happy");
        else
            System.out.println("Not happy");
    }

    public static boolean isHappyNumber(int n) {
        Set<Integer> set = new HashSet<>();
        while (set.add(n)) {
            int sum = 0;

            while(n != 0) {
                int digit = n % 10;
                n = n / 10;

                sum += digit * digit;
            }

            if (sum == 1)
                return true;

            n = sum;
        }

        return false;
    }
}