为自定义LinkedList类添加方法

Question

I have been working on this add method for a custom linkedlist lab I am working on. I cannot figure out how to shift values over by one index, once I insert the new node. Here is my source code.

public void add(int index, Object element) throws IndexOutOfBoundsException {
    if(index > size() || index < 0) {
        throw new IndexOutOfBoundsException();
    }

    ListNode newNode = new ListNode(element, null);

    if(head == null) {
        head = newNode;
        return;
    }

    ListNode nextNode = head.nextNode;
    ListNode currNode = head;

    int i = 0;
    while(currNode!= null) {

        if(index == i) {
            break;
        }

        currNode = nextNode;
        //Breaks down here with null pointer exception
        nextNode = nextNode.nextNode;

    }

    currNode = newNode;
    currNode.nextNode = nextNode;
}

Answer 1

It is throwing null pointer as when you are iterating last node, next node points to null. Check for next node point to null also if you have to add new node in last.

Also in your code you are not increasing the value of i always it is iterating the whole list.

Answer 2

I don't really know what you are trying to achieve here, and I agree with @Pritam Banerjee's comment. But an obvious problem in your code is that you are never incrementing i, so you'll never break out of your while loop and at some point you are going to hit the end of your list and nextNode.nextNode is going to be null, hence your exception. (Also note that nextNode.nextNode will be null before currNode is.)