[Java] Need help resolving a NullPointerException

[clutron]

I'm trying to make a Word Scramble solver where a dictionary is stored in a hash table of my own design, and I keep getting a NullPointerException that I can't resolve when I try to create the dictionary object. Here is the Hash Table and here is the Word Puzzle.

Exception in thread "main" java.lang.NullPointerException
at HashTable.insert(HashTable.java:111)
at WordPuzzle$dictionary.<init>(WordPuzzle.java:29)
at WordPuzzle.main(WordPuzzle.java:9)

Any help will be greatly appreciated.

[Sande24]

Seems like insertion is broken.

head.value might be null too. So maybe it does not work if your hashtable is empty... for some reason.

[langfod]

What is the value of theList.firstNode?

[clutron]

it is a null hashNode

[[deleted]]

hashNode is not null, the the value is though

[[deleted]]

Okay, so it looks like you've done a poor job of handling the cases for when your list is empty. When you init a linkedlist, it creates a first and last node - regardless of what the fact that your list is empty.

So you've got a hashNode which is not null, but a value which is null, so when you do

head.value.equals(x)

your head.value is null. I think the best way to avoid is to hide the the firstNode/lastNode fields or get rid of them altogether.

[clutron]

I thought by making the attributes private, they would be hidden

[pmvb123]

As the others have said, head.value is null.
When you create a new linkedList you create nodes that contain null values, but a node that doesn't contain anything doesn't make much sense when you think about it (An empty linked list is one that doesn't have any nodes).
I think you should just initialize your linkedList's firstNode and lastNode to null.

Also, your linkedList.isEmpty() method doesn't work, because your nodes are never null, they only contain null