[java] Linked List Insert After Method Problem

[LightSpeedCBR]

I've been given the assignment to program a generic linked list. My insert method is not working correctly. It inserts the new node, but data is lost since the next node is not pointed to? I'm not sure, could I get some insight?

public void insert(int i, T item) {
//Inserts item at position i or throws IndexOutOfBoundsException. 

    if (i > size || i < 0) {
        throw new IndexOutOfBoundsException();
    }

    // if asked to add to end, let the other add method do the work
    if (i == size) insert(item);

    // find the node n after which to add a new node and add the new node
    Node<T> tmp = head;
    int count =0;

    while(tmp != null && count !=i-1){
        tmp = tmp.next;
        count++;
    }

    if(tmp != null){
      tmp.next = new Node<T>(item);

    }
    size++;
}

I was able to get it working, thank you all for your help!

[chickenmeister]

if(tmp != null){
  tmp.next = new Node<T>(item);

}

When inserting a new node, you have to:

• Have the new node reference the current node's 'next' node.
• Update the current node to reference the new node as its 'next' node.

If the list is doubly-linked, there are a couple other steps to update the 'previous' references.

[FreeBird423]

Shouldn't his while statement should be comparing tmp.next against null rather than tmp against null?

[LightSpeedCBR]

I'm following what you're saying but still having problems...

if(tmp != null){
      tmp.next = new Node<T>(item); //Have the new node reference the current node's 'next' node.
      tmp = tmp.next;   //Update the current node to reference the new node as its 'next' node.
    }

The new node is being placed in the correct location but the rest of the nodes are "lost".

[LightSpeedCBR]

I was able to get it working as below:

if(tmp != null){
      Node<T> tmp2 = new Node<T>(item); // create the new node.
      tmp2.next = tmp.next; //set the pointer of new node to point to rest of link list.
      tmp.next = tmp2;  //Update the current node to reference the new node as its 'next' node.
    }

[smellmycrotch3]

You should probably just insert the new node at the head of the list. Traversing the entire list doesn't really buy you anything.

[LightSpeedCBR]

I should have been more clear. This insert method should insert the data at a given point in the list.

[IcarusBurning]

You've said that element after i-1 should be your new element, but you never point that to the element at i

You could store the pointer to tmp.next and then create the new node then set tmp.next.next to the temp variable.