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Marking an optional member variable as NonNull

One of the variables of the String class of my class is optional. Does it make sense to mark this with the Lombok @NonNull annotation?

I would like to ask the same question in case the member variable is Map instead of String. Will the answer change?

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An additional point is the creation of a free API. The field is not and should not be part of the API.

What's the difference for you between Optional<Object> obj

and Object obj

in the fields?

Both fields can be annotated with @NotNull

. Annotating a field with @NotNull

will give you the same result as annotating Optional

, but without additional calls like ifPresent()

. If you want Optional

to use chaining to apply operations to a field, you are using Optional

incorrectly. There is no reason to use it Optional

in the field.



You can read more on the openjdk mailing list for an optional discussion .

This option allows you to create a free API mail.openjdk

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Yes, you must mark each variable Optional

as @NonNull

.

An optional variable must never be null. Stuart Marks rules about using optionals start with:

  • Never, never, use null for an optional variable or return value.

If you are writing @NonNull

, then you will get help not to break this important rule.



If you don't write @NonNull

, you only have your own personal discipline so that you don't make mistakes, and clients can make mistakes too.

Hence, you should write @NonNull

, which serves as machine readable and machine tested documentation, that a variable should never be null.

This applies not only to fields (member variables), but wherever you use Optional

.

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