Re: NullPointerException, IllegalArgumentException, or AssertionError for null constructor argument

Patricia Shanahan <>
Fri, 28 Dec 2007 14:41:33 -0800
Eric Sosman wrote:

Daniel Pitts wrote:

I have a constructor that takes a String argument. I'd like to throw
an exception if the constructor is invoked with a null argument, but
I'm not sure which instruction I should use.
NullPointerException is technically accurate, since it is a null
pointer, but it is also an IllegalArgumentException. I think that
IllegalArgumentException is more specific, so I'll probably go with
that, but wanted opinions.

The third option is AssertionError. I could just use assert
arg!=null, and that could be enough. This is for a personal project,
so it doesn't *really* matter, but at the same time its good practice
for me to think about these sort of things :-)

    IllegalArgumentException would get my vote, with a possible
last-minute in-the-voting-booth defection to NullPointerException.
AssertionError is the candidate whose placards I'd tear down, no
matter what the election authorities might think.

Agree with this, with the possible addition of a merger between the two
acceptable options - throw an IllegalArgumentException with a
NullPointerException as cause. However, IllegalArgumentException with a
clear message should normally do the job.


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