Question

I’m trying to create a method that will add a node to my linked list. The method takes an int (to specify where the new link should go) and String (because my linked list holds strings). I wrote some code that I thought would add a link at specific point in my list, however when I print my list after supposedly adding a new node, I see that the new node has not been added. I’m pretty surprised because I was careful about testing the behavior of my code as I was writing it, and the add method seems to do what I expect–but the newly printed list isn’t reflecting the changes after adding a new link. Can anyone tell where I’m going wrong :/

ps: the names of the classes and methods are not up for debate, my teacher chose them and that’s how they must stay.

thanks!

Test Linked List

class LinkedListTest 
{
    public static void main(String[] args) 
    {
            LinkedList list = new LinkedList();

            list.insertFirst("cat");
            list.insertFirst("dog");
            list.insertFirst("fish");
            list.insertFirst("cow");
            list.insertFirst("horse");
            list.insertFirst("pig");
            list.insertFirst("chicken");

            list.add(3, "mouse");

            list.print();
    }   
}

Linked List Class

public class LinkedList 
{
    private Link first;

    public LinkedList() 
    {
        first = null;
    }

    public void insertFirst(String word)
    {
           Link link = new Link(word);
           link.next = first;
           first = link;

           System.out.print(first.item + " ");
    }

    public String deleteFirst()
    {   
        Link temp = first;
        first = first.next;
        return temp.item;
    }

    public String get(int index)
    {
        Link current = first;
        while (index > 0) 
         {
             index--;
             current = current.next;
         }

         return current.item;           
    }

    public void add(int index , String someString)
    {

        Link current = first;

        while (index>0)
        {
            index--;
            current = current.next;
        }

    Link newLink = new Link(someString);
    newLink.next = current;
    current = newLink;

    }

    public void print()
    {
        System.out.println("-----------PRINTING LIST------------");
        Link current = first;
        while(!(current==null))
        {
            System.out.println(current.item);
            current = current.next;
        }
    }
}

Link Class

public class Link 
{   
    public String item;
    public Link next;

    public Link(String theItem) 
    {
        item = theItem;
    }
}

Answer 1

newLink.next = current;
current = newLink;

The above code in your add method of LinkedList class should be: –

newLink.next = current.next;
current.next = newLink
current = newLink;

I hope this might solve your problem. You need to set two next links to insert a node in the middle. One at the current node pointing the next node, and one at the prevoius node pointing to the current node.