Null pointer exception on .iterator() call

Question

I'm getting a strange NullPointerException, evidently thrown by the following line of code:

Iterator<Note> it = notes.iterator();

I've checked, and at the time the java.util.TreeSet notes is always non-null (with 15 elements). The TreeSet API says nothing about iterator() throwing NullPointerExceptions. What else could be going here?

Can you post the code where you populate the tree and where you're instantiating notes? — Jaime Garcia
– Jaime Garcia, Commented Mar 14, 2010 at 22:35
Can we see the stack trace? Are you 100% sure the NPE was thrown at this line? — skaffman
– skaffman, Commented Mar 14, 2010 at 22:43

Tom Hawtin - tackline · Accepted Answer · 2010-03-14 22:34:54Z

2

If notes is not null then:

You are mistaken (never discount this option).
The implementation of notes is broken.
You are using the implementation incorrectly - for instance having multiple threads access it at once.

answered Mar 14, 2010 at 22:34

Tom Hawtin - tackline

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1 Comment

skaffman Over a year ago

If the NPE came from the line he says, then (1) is the only explanation that I can see. The other two options would cause the NPE elsewhere.

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