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;

Julien Lebosquain · Accepted Answer · 2011-04-03 10:55:04Z

8

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.

answered Apr 3, 2011 at 10:55

Julien Lebosquain

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Comments

aldrin · Accepted Answer · 2011-04-03 11:09:48Z

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

answered Apr 3, 2011 at 11:09

aldrin

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