Why can't I compute a constant annotation parameter?

Question

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

See also here for possible solutions: http://stackoverflow.com/questions/13253624/how-to-supply-enum-value-to-an-annotation-from-a-constant-in-java — atom88, Jan 19 '17 at 16:22

score 4 · Answer 1 · edited Sep 13 '12 at 09:07

4

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.

edited Sep 13 '12 at 09:07

Asciiom

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answered Feb 05 '12 at 03:04

Jeff Axelrod

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see also here for possible solutions: http://stackoverflow.com/questions/13253624/how-to-supply-enum-value-to-an-annotation-from-a-constant-in-java – atom88 Jan 19 '17 at 16:23

Why can't I compute a constant annotation parameter?

1 Answers1