Implement this java method public void addE item The method

Implement this java method, public void add(E item). The method behaves like this: when the input does not exist in the linked list, add it at the front; otherwise remove the existing one from the list and reinsert it to the front.

Solution

import java.util.Iterator;

public class LinkedList<E> extends AbstractList<E> {
   private ListNode front; // refers to first node in list (null if empty)
  
   // Constructs a new empty list.
   public LinkedList() {
       front = null; // null front means empty
   }
  

   public void add(int index, E value) {
       if (index == 0) {
           // insert at the front
           front = new ListNode(value, front);
       } else {
           // insert in middle/end; walk to node before the one to insert
           ListNode current = goTo(index - 1);
           ListNode newNode = new ListNode(value, current.next);
           current.next = newNode;
          
           // shorter version of the above code
           // current.next = new ListNode(value, current.next);
       }
   }
  

   public void remove(int index) {
       if (index == 0) {
           // removing from the front
           front = front.next;
       } else {
           ListNode current = goTo(index - 1);
           current.next = current.next.next; // deletes the node
       }
   }

   public void set(int index, E value) {
       ListNode current = goTo(index);
       current.data = value;
   }
  

   private class LinkedListIterator implements Iterator<E> {
       private ListNode current; // current position in list

       public LinkedListIterator() {
           current = front;
       }

       public boolean hasNext() {
           return current != null;
       }

       public E next() {
           E result = current.data;
           current = current.next;
           return result;
       }

       // not implemented for now
       public void remove() {
           throw new UnsupportedOperationException();
       }
   }  
}