Question

I have to create an array of linked lists for a class in order to store a graph (adjacency list). We have to use Java. I can create the array and instantiate each linked list, but when I go to add the first elements to each one, every linked list gets changed, not just the one at the index of the array.

Node [] adjList;
for(i=0;i<adjList.length;i++)
    adjList[i] = new Node(0,0,null);

this instantiates each new linked list [Node is my own class, with constructor Node(int head, int data, Node next) and extends LinkedList]

then i go to add the first values to each node:

for(i=0;i<adjList.length;i++)
    adjList[i].setHead(i+1); //  numbers 1 to end are the graph vertices

or

for(i=0;i<adjList.length;i++)
    adjList[i].add(new Node(i+1,0,null);

I use print statements to debug the code
at the end of these loop I print off each Linked List, but for each one, the values come out to be the final one

ie. if adjList.length = 2, it would print out

[3,0,null] // adjList[0]
[3,0,null] // adjList[1]
[3,0,null] // adjList[2]

edit: here is the Node class

import java.util.LinkedList;
public class Node extends LinkedList{
    private static int head;
    private static int data;
    private static Node next;

    public Node(int h,int d,Node n) {
        head = h;
        data = d;
        next = n;
    }
    public int getHead(){ // getNext() and getData() are the same
        return head;
    }
    public void setHead(int h){ // setNext() and setData() are basically the same
        head = h;
    }
}

Answer 1

You have probably declared something within Node as static, so every instance ends up with the same shared value, rather than having its own value. However, this is just a guess – please post the code of Node so we can see what the problem really is…