Head of 2 different linked lists getting changed to same value

Question

I am creating a chained hash table that uses my own LinkedListclass to handle collisons. Here is where my issue is occuring: I start with an array of LinkedLists, my "hash table", intially set to null. When i wish to add a word, if the desired location is null, I create a new LinkedList, place it in that array index. I then create a new LinkedListNode and set the head of the new LinkedList to the new node.

My issue is occuring here: Whenever I set the head of my new LinkedList to my new LinkedListNode all of my previously created linkedlists also have their head changed to the new node.

My debugger shows that I am truly creating new linkedlists every time. I was afraid each array index was just pointing to a single array, but that is evidently not the issue. Below is all the relevant code

public class SetOfStrings {

private int arraySize;
private LinkedList[] mainArray;
private int totalCount;

//other methods here

public boolean add(String toAdd)
{
    int hashToAdd = hash(toAdd);
    int wasFound = contains(toAdd);
    if(wasFound> 0)
    {
        return false; // means its already in the table
    }
    if(mainArray[hashToAdd]== null)
    {
        mainArray[hashToAdd] = new LinkedList();
        ListNode newHead = new ListNode(toAdd);
        mainArray[hashToAdd].setHead(newHead);
        totalCount++;
        return true;
    }
    ListNode currentHead = mainArray[hashToAdd].getHead();
    ListNode newNode = new ListNode(toAdd);
    newNode.setNext(currentHead);
    mainArray[hashToAdd].setHead(newNode);
    totalCount++;
    return true;

}

---

public class ListNode {

private String thisString;
private ListNode next;

public ListNode(String setString)
{
    thisString = setString;
    next = null;
}

---

public class LinkedList {

private static ListNode head;
private static  int count;
private static  ListNode currentPosition;

// other methods here

public  void setHead(ListNode newNode)
{ head = newNode;}

SUMMARY: Whenever I set the head of a Linked List to a new node, it changes the head of all my linked lists to point to the same new node

Answer 1

You are declaring your head as static. This means that it is shared between all instances of the LinkedList class. Removing the static keyword should fix the issue you described.