public void addElement(ValueType value) {
        if (amount == 0) {
            SetElement<ValueType> current = new SetElement<>(value);
            head = current;
            tail = current;
            amount++;
        } else {
            if (!exist(value)) {
                SetElement<ValueType> current = new SetElement<>(value);
                tail.connectNext(current);
                tail = current;
                amount++;
            }
        }
    }