Useful message about NullPointerException

Florian Weimer fweimer at
Tue Jan 27 13:14:44 UTC 2015

On 01/21/2015 01:45 PM, pike wrote:
> We frequently see NullPointerException in our logs. It's really a big
> headache when we see a NullPointerException and it is encapsulated in
> another exception as we don't know which object is null and it is throwing
> an Exception. Is there any way we can get to know the object type or the
> object variable name where the object is null and it is throwing a
> NullPointerException?

The line number gives you the position in the source code, and from
that, you can usually figure out the static type.  If this is not
helpful in your case, you need to say why (no debugging information?
multiple candidates per line?).

The dynamic type is a different matter though, because null has no
specific type at run time.  It may be possible to provide type
information in theory, at a cost, but this would best be prototyped
through byte code rewriting.  Nullable annotations would also help to
pin-point location of the first leak, and you could record that
(including a stack trace) if you want something really fancy.  Whether
it is helpful for legacy code, I don't know.  There should be some
research projects out there covering this area.

Florian Weimer / Red Hat Product Security

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