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java annotations lombok

Why would I use Lombok-Annotation @NonNull?

发布于 2020-03-29 21:02:01

Lombok offers the annotation @NonNull which executes the nullcheck and throws a NPE (if not configured differently).

I do not understand why I would use that annotation as described in the example of that documentation:

private String name;
public NonNullExample(@NonNull Person person) {
    super("Hello");
    if (person == null) {
      throw new NullPointerException("person is marked @NonNull but is null");
    }
    this.name = person.getName();
  }

The NPE would be thrown anyway. The only reason here to use the annotation imo is if you would want the exception to be different from a NPE.

EDIT: I do know that the Exception would be thrown explicitly and thus 'controlled', but at least the text of the error message should be editable, shouldn't it?

Questioner
metters
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mernst 2019-06-25 00:00

Writing a type annotation such as @NonNull serves several purposes.

  • It is documentation: it communicates the method's contract to clients, in a more concise and precise way than Javadoc text.
  • It enables run-time checking -- that is, it guarantees that your program crashes with a useful error message (rather than doing something worse) if a buggy client mis-uses your method. Lombok does this for you, without forcing the programmer to write the run-time check. The referenced example shows the two ways to do this: with a single @NonNull annotation or with an explicit programmer-written check. The "Vanilla Java" version either has a typo (a stray @NonNull) or shows the code after Lombok processes it.
  • It enables compile-time checking. A tool such as the Checker Framework gives a guarantee that the code will not crash at run time. Tools such as NullAway, Error Prone, and FindBugs are heuristic bug-finders that will warn you about some mis-uses of null but do not give you a guarantee.

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