CODEWITHSUNDEEP
javaannotations
Jeff Axelrod
Jeff Axelrod

Reputation: 28188

Why can't I compute a constant annotation parameter?

Why does the following code compile:

final String name = "works";
@Provides @Named(name) String provideAboutTitle() {
   return "ABC";
}

But the following code fails (at least with Eclipse's compiler):

final String name = UUID.randomUUID().toString();
@Provides @Named(name) String provideAboutTitle() {
   return "ABC";
}

Eclipse's compiler returns the following error:

The value for annotation attribute Named.value must be a constant expression

Upvotes: 4

Views: 1482

Answers (1)

Jeff Axelrod
Jeff Axelrod

Reputation: 28188

The constant expression Eclipse demands in the error message is a compile-time constant expression (not just a final variable) and the method call UUID.randomUUID().toString(); needs to be evaluated at run-time.

While you can write dynamic annotation values using JavaAssist at runtime, you will lose "easy to read" feature of the annotations.

Upvotes: 4

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