CODEWITHSUNDEEP
javanullpointerexception
Jieun Chon
Jieun Chon

Reputation: 139

null pointer exception from my code from the while loop

I decleared free block like 

private DoublyLinkedList freeblock = new DoublyLinkedList();

and I initialize the freeblock in the constructor.

freeblock.add(new DoublyLinkedList.Node(null, null, 0, initBlockSize));

inside of one of method of my class, (below is part of my method.) I get null pointer exception. I think the while loop has a problem. Can anyone help me to solve this problem?

symptom: java.lang.NullPointerException at LinearMemPool.enlarge(LinearMemPool.java:220)

private void enlarge(int addSize) {

DoublyLinkedList.Node node = freeblock.head;
    while (node.next != null) { 
            node = node.next;

    }
}

Upvotes: 0

Views: 375

Answers (3)

Rika
Rika

Reputation: 796

First check to see freeblock.head is null because most likely it is: 

if(node!=null){

   while(node.next!=null){
   ....
}

else{
 System.out.println("Freeblock is null but why.....");

}

You probably should do this normally if the freeblock.head can ever be null. And just for cleaning up purposes:

void newMethod(Node node, int size){
 if(node!=null)
   enlarge(size);
 else{
   System.out.println("Freeblock is null");
  }

}

Upvotes: 0

But I'm Not A Wrapper Class
But I'm Not A Wrapper Class

Reputation: 14286

Your enlarge method seems a bit dangerous. Try changing the null check to:

private void enlarge(int addSize) {
    DoublyLinkedList.Node node = freeblock.head;
    while (node != null) { 
        node = node.next;
    }
}

As for the reason why your head is null, I'd debug the freeblock.add(...) method.

Upvotes: 0

Joop Eggen
Joop Eggen

Reputation: 109597

Evidently freeblock.head is null. Look what add does.

Upvotes: 1

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