How to throw a null pointer exception and where [duplicate]

Question

When I have a potential null input... is it better to always check for it:

public void doSomething(String str) { if (str == null) throw new NullPointerException(); processData(str); }

or pass on the invalid data, and wait for "processData()" to throw the nullPointerException:

public void doSomething(String str) { processData(str); }

it depends - if processData is an internal function (not accessible as a public interface), it might not do a null pointer check. Even if it does, it depends if you have code before processData that needs to run. — ronalchn
– ronalchn, Commented Oct 8, 2015 at 11:44
I think, need to check first, if not NULL then pass ahead. so that in future any further modification comes on other module not get affected by null pointer. — Vishal Gajera
– Vishal Gajera, Commented Oct 8, 2015 at 11:47
There are also some annotations for non-null parameters. But the trend seems that non-null is in general assumed. In java 8 use Optional<String> for possibly missing values. So a javadoc comment would be entirely sufficient. — Joop Eggen
– Joop Eggen, Commented Oct 8, 2015 at 11:48

wero · Accepted Answer · 2015-10-08 11:48:26Z

This is opinionated, but imho it is better to throw it in the first layer:

If you got a stracktrace and see a NPE (deep down) inside a library implementation it is not clear if it was caused by a bug in the library or by your illegal argument.

For the same reason I would recommend to use a descriptive IllegalArgumentException instead of a NPE:

if (str == null) throw new IllegalArgumentException("str is null");

(and give str a better name, too).

I just want to add that above code can be rewritten as Objects.requireNonNull(str,"str is null");

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