Declaring a variable as more than one interface [duplicate]

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
– Jason C, Commented Jul 24, 2016 at 21:41
Do you mean <T extends Member & AnnotatedElement> void method(T o)? — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jul 24, 2016 at 21:43
@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
– Jason C, Commented Jul 24, 2016 at 21:44

resueman · Accepted Answer · 2016-07-24 21:43:38Z

3

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

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

answered Jul 24, 2016 at 21:43

resueman

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1 Comment

Jason C Over a year ago

Whoa, cool. Thanks!

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