Java generics SuppressWarnings(“unchecked”) mystery

Question

Why does code alternative(1) compile without warnings, and code alternative(2) produce an \"unchecked cast\" warning?

Common for both:

class Foo         


        

Answer 1

I was able to reproduce the behavior with this simplified setup:

class Bar {
   @SuppressWarnings("unchecked")
   Bar() {
      T[]dummy = (T[]) EMPTY_ARRAY;
   }

   private static final Object [] EMPTY_ARRAY = {};
}

As Brian suggested, it seems to be a bug in the compiler. Additionally, this behavior is restricted to Arrays - replacing the EMPTY_ARRAY with an Object and casting it to a T does not issue a warning as expected.

java version "1.7.0_09"
Java(TM) SE Runtime Environment (build 1.7.0_09-b05)
Java HotSpot(TM) 64-Bit Server VM (build 23.5-b02, mixed mode)