How to Flip a Double Linked List in java and put it into a new List

I wanted to flip a Double Linked List and put it into a new List. But I don’t know how to solve the Problem. My Code looks like this and I think it makes sense, but it doesn’t work at all.

getPred = previous
getSucc = next

    public DoublyLinkedList fliping()
    {
        DoublyLinkedList newList = new DoublyLinkedList();
        Element current = last;
        Element toInsert = newList.first;
        while(current != null)
        {
            current.disconnectPred();
            Element temp = current.getPred();
            Element temp2 = current.getPred().getPred();
            if(toInsert == newList.first)
            {
                temp.connectAsSucc(temp2);
                temp2.connectAsPred(temp);
                toInsert.connectAsSucc(temp);
                newList.size++;
            }
            if(temp2 == null)
            {
                temp.connectAsSucc(temp2);
                toInsert.connectAsSucc(temp);
                newList.size++;
            }
            temp.connectAsSucc(temp2);
            temp2.connectAsPred(temp);
            toInsert.connectAsSucc(temp);
            toInsert.connectAsPred(temp2);
            toInsert = toInsert.getSucc();
            current = current.getPred();
            newList.size++;
            size--;
        }
        return newList;
    }

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Element.getPred()" because the return value of "Element.getPred()" is null
    at DoublyLinkedList.fliping(DoublyLinkedList.java:282)
    at Testumgebung.testDoublyLinkedList(Testumgebung.java:35)
    at Testumgebung.main(Testumgebung.java:7)

I tried to disconnect the last element and the second last element. Than i tried to connect them to each other and put them togeter, as the first and second element into the new List

>Solution :

If your DoublyLinkedList implements the interface java.util.List I would first ensure that you can copy it (e.g. with a copy-constructor that initializes it with any other Collection or List – don’t implement the clone method, too much hassle with that!).

Then simply use the method java.util.Collections.reverse(List<?>) on a 1:1 copy of your original list.