Having issue with 'Null pointer access' in Java

Question

if(key == '1'){//insert at ->right.right
    BinaryNode tempPointer = root;

    while(tempPointer != null){
        tempPointer = tempPointer.right;
    }
    BinaryNode newNode = new BinaryNode(x);
    newNode.right = null;
    newNode.left = null;
    size++;
    lastNode = newNode;
    newNode.parent = tempPointer;
    tempPointer.right = newNode;
}

It keeps saying termPointer can only be null at this location. I can't figure out why though.

This also fails:

newNode.parent = tempPointer.parent; //'tempPointer can only be null here'
tempPointer = newNode;

Answer 1

Your while loop will only end when tempPointer is null . You don't set tempPointer to any other value after the loop, so it will stay null until the end of the function.

Answer 2

You actually want a look ahead pointer that peeps to the right of the current node. Something like,

BinaryNode tempPointer = root;
lookaheadPointer = root;
while(lookaheadPointer != null) {
  tempPointer = lookaheadPointer;
  lookaheadPointer = tempPointer.right;
}

In your current code, the tempPointer is null at the end of the loop, as pointed out by @Julien