JAVA Immutablilty, Copying a Linked List

Question

I am tasked with creating a Linked List class in Java that MUST be immutable. This has been accomplished exactly the same as on here:

https://www.geeksforgeeks.org/linked-list-set-1-introduction/

Among other methods, I need an addToList method that adds a value or multiple values to the tail of the Linked List. Since the Linked List is immutable, adding to it should create a copy of the Linked List (i.e. a new LinkedList object with the same contents) and only add the desired values to the newly created copy.

The copy function is where I need help. Below is the copyList function, partially completed. I am traversing each Node in the LinkedList and printing out the data successfully. Now I need to assign that data to the corresponding element in the clonedList (the new copy). Please see the image below.

public LinkedList<T> copyList(LinkedList<T> toCopy) {
    Node n = toCopy.head;
    LinkedList clonedList = new LinkedList<T>();

    while(n != null) {
        System.out.println("Copying: " + n.data);
        /*code here(?) to assign elements to clonedList,
        but how?
         */
        n = n.next;

    }

    return clonedList;


}

Does this answer your question? [In what situations is the CopyOnWriteArrayList suitable?](https://stackoverflow.com/questions/17853112/in-what-situations-is-the-copyonwritearraylist-suitable) — Adwait Kumar, Dec 18 '19 at 18:26
Does this answer your question? [Making a deep copy of a LinkedList in java](https://stackoverflow.com/questions/22751588/making-a-deep-copy-of-a-linkedlist-in-java) — NegativeFriction, Dec 18 '19 at 18:27
Please provide the code you need help with and state more precisely what the problem is. — emilaz, Dec 18 '19 at 18:48

score 0 · Answer 1 · answered Dec 18 '19 at 18:25

0

I'm not much for Java, but can't you just do

clonedList.add(n.data)

in your while loop to create a deep copy?

answered Dec 18 '19 at 18:25

NegativeFriction

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I cannot because (as far as I know), ".add" works on Arrayists, sets etc. This LinkedList is a class of its own, so Java doesn't know what it means when I write clonedList.add(... – Quentin James Dec 18 '19 at 18:36
Per my googling, I think you're mistaken. https://www.geeksforgeeks.org/java-util-linkedlist-add-method-in-java/ – NegativeFriction Dec 18 '19 at 18:38
1

@NegativeFriction I think the point is he has his own implementation without an `add` method. – cbryant02 Dec 18 '19 at 18:43
1

I am working with a class I created called "LinkedList", I did not import it from java.util.LinkedList. That's why I can't use .add – Quentin James Dec 18 '19 at 18:50

cbryant02 · Answer 2 · 2019-12-18T18:50:13.940

If you don't need a deep copy, you should just be able to set the head of the cloned list to that of the original, e.g.:

LinkedList<T> clonedList = new LinkedList<>();
clonedList.head = toCopy.head;

Otherwise, construct a new Node on each loop iteration and add it to the cloned list. It sounds to me like you have your own LinkedList implementation without an add method, so either write one or replace the method call in the example.

Node<T> n = toCopy.head;
LinkedList<T> clonedList = new LinkedList<>();

while(n != null) {
    Node<T> nClone = new Node<>(toCopy.data);
    clonedList.add(nClone);
    n = n.next;
}

Also, this method should probably either be a constructor or a static method. It doesn't make sense to require an instance for a method that doesn't modify the list's state.

JAVA Immutablilty, Copying a Linked List

2 Answers2