How do I avoid "potential null pointer access" when using Preconditions.checkNotNull()?

Question

Eclipse gives me the warning "Potential null pointer access: The variable ann may be null at this location":

SomeAnnotation ann = type.getAnnotation( SomeAnnotation.class );
Preconditions.checkNotNull( ann, "Missing annotation on %s", type );

for( String value : ann.value() ) { // <-- warning happens here
}

I'm using Eclipse 3.7 and Guava. Is there a way to get rid of this warning?

I could use SuppressWarnings("null") but I would have to attach it to the method which I feel would be a bad idea.

May this helps : http://stackoverflow.com/questions/6772129/strange-java-compiler-warning-incorrect-potential-null-access-warning — user2336315, Jun 06 '13 at 09:38
I tried `SomeAnnotation.value()` which returns `String[]`, and no null warning. What's your `SomeAnnotation` looks like? — 卢声远 Shengyuan Lu, Jun 07 '13 at 10:43

score 2 · Answer 1 · answered Jun 07 '13 at 00:39

2

You could stop using Eclipse.

Hey, it's a solution. It may not be the one you want, but it solves the problem and isn't really a bad solution.

More seriously, you could:

adjust compiler warning settings,
use SuppressWarnings at method or class level,
use a more modern compiler (apparently later versions do not trigger this for simple cases),
rewrite your code to work and assign the return value of checkNotNull to ann.

answered Jun 07 '13 at 00:39

haylem

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I agree that it's a solution but I would prefer one which just changed the code instead of changing the way 20 people are used to work :-) – Aaron Digulla Jun 07 '13 at 07:59
2

It's funny how people downvote this just because they don't like the first sentence, and discard the valid suggestions following it. And it's still a solution too. – haylem Aug 10 '16 at 16:52

Aaron Digulla · Accepted Answer · 2016-08-15T16:11:21.907

Eclipse e4 has much better support for null checks and resource tracking in the compiler.

Another solution is writing your own version of checkNotNull like so:

@Nonnull
public static <T> T checkNotNull(@Nullable T reference) {
  if (reference == null) {
    throw new NullPointerException();
  }
  return reference;   
}

Now you can use this approach:

SomeAnnotation ann = Preconditions.checkNotNull( type.getAnnotation( SomeAnnotation.class ) );

(I've omitted the version of checkNotNull() which take error messages; they work in the same way).

I'm wondering why Guava doesn't do that since they already use these annotation elsewhere.

How do I avoid "potential null pointer access" when using Preconditions.checkNotNull()?

2 Answers2