Looking into another question I bumped into this intriguing behavior of the 1.8.0_112 Sun-Oracle compiler (I have not tested with others):

import java.util.List;

interface Alpha<T> {
   List<Integer> intList();
}

interface Beta {
   List<Integer> intList();
}

class Main {

   public static void main(String[] args) {

      Alpha rawAlpha = null;
      Alpha<Character> charAlpha = null;
      Alpha<?> qmAlpha = null;
      Beta beta = null;

      for (Integer i : charAlpha.intList()) {}
      for (Integer i : qmAlpha.intList()) {}
      for (Integer i : beta.intList()) {}
      for (Integer i : rawAlpha.intList()) {}
   }
}

The compiler only fails at the last for loop:

error: incompatible types: Object cannot be converted to Integer
      for (Integer i : rawAlpha.intList()) {}
                                       ^
1 error

So despite that intList() return list type List<Integer> in Alpha does not depend on the type parameter T, it seems that the <Integer> is erased at compilation time.

Notice that if we declare a non-generic interface Beta that would be, in theory, equivalent to making reference to the raw Alpha, there is no issues.

Is this the expected behavior? can some one point out the paragraph on the language spec that would cover this point? If this is not a bug at the very least it seem rather anti-intuitive and non-productive; perhaps is done for the sake of back-comparability?.