Joiner.join(Object[]) doesn't accept null but is annotated with @Nullable

a4baad35 introduces @Nullable at Joiner.join(@Nullable Object[] parts) but actual code would throw a NullPointerException.

[jbduncan]

@xihongshi6 In this situation, the right thing to do is to annotate the array like so:

public void someMethod(Object @Nullable [] array) {
}

Here, it tells us that the array itself (the [] part) can be null, whereas the elements inside cannot.

Likewise, to say that both the array itself and its elements can be null, one would do this:

public void someMethod(@Nullable Object @Nullable [] array) {
}

I agree that it is ambiguous! But I think it’s a limitation of how arrays and annotations work with each other in Java.

If you have any more Guava questions, may I suggest posting them over at StackOverflow? I look at the <kbd>guava</kbd> tag there often, so if you post with that tag, then I’ll be likely to see it. Alternatively, if you have any questions that are just Java-related, post them under the <kbd>java</kbd> tag (I don’t monitor questions with that tag), or send me an email. You can find my email address on my GitHub profile. 😃

[jbduncan]

@xihongshi6 I don’t know about others, but it’s a rule that I understand anyway.

All it is saying is the array cannot be null, but any of the objects in the array can be null.

The reason why is because the @Nullable annotation is annotating the Object part of the array, rather than the [] part.

So this is allowed:

Joiner.on(" ").join(new Object[]{ 1, null, "cat" });

But this is not allowed:

Joiner.on(" ").join(null);

I hope this helps. 😃