If only one element in a hashset, how can I get it out?

Question

HashSet<Integer> set = new HashSet<Integer>();
set.add(1);

How can I get the 1 out? I can do it by for(integer i : set). Do you have another idea to solve the problem?

My specified problem is "Given an array of integers, every element appears twice except for one. Find that single one." I want to use add elements into set if the set doesn't contain it and remove existed element during loop. And the last remain element is answer. I don't know how to return it.

    public static int singleNumber(int[] A) {
    HashSet<Integer> set = new HashSet<Integer>();
    for (int a : A) {
        if (!set.contains(a)) {
            set.add(a);
        } else {
            set.remove(a);
        }
    }
    /**
     * for(Integer i : set) { return i; }
     *return A[0];//need one useless return
    /**
     * while(set.iterator().hasNext()) { return set.iterator().next(); }
     * return A[0];//need one useless return
     */
    return set.toArray(new Integer[1])[0];
}

Answer 1

set.iterator().next()

Do so only if you are sure there is an element in the set. Otherwise next() will throw an exception.