Question

hi guys, could someone tell my where this is going wrong please, its adding into a double linked list, i have another method to add at the end which is working but the rest of this??

thanks

public boolean add(int index, Token obj) {
       if(obj == null) {
           throw new NullPointerException();
       }
       if (index < 0 || index > this.size()-1) {
           throw new IndexOutOfBoundsException();
       }
       // new node to add
       Node toADD = new Node(null,null,obj);
      
       //insert at the beginning of the list
       if(index == 0) {
          
           // make the next of the new node point to the previous head, and previous to null
           toADD.next = head;
           toADD.prev = null;
           //change the previous of head to the new node
           if(head != null) {
               head.prev = toADD;
           // set the new node to be the head;
           head = toADD;
           size++;
           }
       if(index >1) {
          
           for(int i =1; i<= index; i++ ) {
               if(index == i) {
                   Node oldNode = this.getNode(i);
                   toADD.prev = oldNode.prev;
                   oldNode.prev = toADD;
                   toADD.next = oldNode;
                   toADD.prev.next = oldNode;
                   size++;
                   }
       if(index == this.size()-1) {
           this.add(obj);

Answer 1

I can't See Your Full Code so, i can't Judge where You are doing wrong But to add At From Of doubly linked list simply do This.

 // Adding a node at the front of the list public void push(int new_data) {     /* 1. allocate node     * 2. put in the data */         Node new_Node = new Node(new_data);     /* 3. Make next of new node as head and previous as NULL */     new_Node.next = head;   new_Node.prev = null;   /* 4. change prev of head node to new node */   if (head != null)               head.prev = new_Node;   /* 5. move the head to point to the new node */         head = new_Node; } 

To Add After a Given Node use this method

 /* Given a node as prev_node, insert a new node after the given node */ public void InsertAfter(Node prev_Node, int new_data) {     /*1. check if the given prev_node is NULL */    if (prev_Node == null) {                System.out.println("The given previous node cannot be NULL ");          return;         }       /* 2. allocate node     * 3. put in the data */         Node new_node = new Node(new_data);     /* 4. Make next of new node as next of prev_node */     new_node.next = prev_Node.next;         /* 5. Make the next of prev_node as new_node */         prev_Node.next = new_node;      /* 6. Make prev_node as previous of new_node */         new_node.prev = prev_Node;      /* 7. Change previous of new_node's next node */        if (new_node.next != null)              new_node.next.prev = new_node; } 

Hope This Helps.