Declaring a variable as more than one interface

Question

Is there a way to specify a type that is more than one interface, and have the type check be done at compile time?

Example: Let's say I have a method like

void method (Object o) { ... }

But I want to constrain o at compile time to something that implements both java.lang.reflect.Member and java.lang.reflect.AnnotatedElement (e.g. Class, Field, Method, etc.), and access the methods of both interfaces ideally without casting o.

There are plenty of ways to do this at run-time, I'm just specifically curious about a compile-time check.

@mszymborski Sure but I can't modify existing classes (like `java.lang.reflect.Field`) to implement it. — Jason C, Jul 24 '16 at 21:41
@SotiriosDelimanolis Whoa. I had no idea you could do that. That's exactly the answer, you should post it. Thanks! (Sorry, resueman beat you to it!) — Jason C, Jul 24 '16 at 21:44

score 3 · Accepted Answer · answered Jul 24 '16 at 21:43

3

Yes, you can do that with generics. Define your method like this:

<T extends Member & AnnotatedElement> void method (T o){ /* ... */ }

answered Jul 24 '16 at 21:43

resueman

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[Whoa, cool.](http://www.reactiongifs.com/r/2013/10/tim-and-eric-mind-blown.gif) Thanks! – Jason C Jul 24 '16 at 21:46

Declaring a variable as more than one interface

1 Answers1