//insert, find, delete
    public void insert(S key, T element) {
        //check if load factor is too big
        double resize = (double) totalKeys / (double) array.length;
        if (resize > THRESHOLD) {
            resize();
        }
        //create new node
        Node<T> temp = new Node<T>();
        Node<T> prev = new Node<T>();
        temp.key = key;
        temp.element = element;
        //find a place to put it
        // hash function, key % tableSize % hashcode
        int slot = key.hashCode() % array.length;
        int hash = key.hashCode() % getPrime();
        if (array[slot] == null) {
            array[slot] = temp;
            totalKeys++;
        } else {//double hashing
            prev = array[slot];
            while (array[slot] != null) {
                prev = array[slot];
                slot += hash;
                slot %= array.length;
            }
            array[slot] = temp;
            prev.nextNode = temp;
            totalKeys++;
        }
    }