inconsistent generic types behaviour when compiling together vs. separate

[Peter Levart]

Here's an example:

Create an empty directory and copy into it the following two sources:

Ref.java:

     public class Ref<T> {
         final RefQueue<? super T> queue = new RefQueue<>();

         public static void main(String[] args) {
             Ref<Object> r = new Ref<>();
             RefQueue<Object> q = r.queue;
         }
     }

RefQueue.java:

     public class RefQueue<T> {
     }

Then execute:

     mkdir out
     javac -d out Ref.java

This compiles fine and produces two class files in out directory:

     Ref.class
     RefQueue.class

Now do the following:

     rm RefQueue.java
     mkdir out2
     javac -cp out -d out2 Ref.java

Which produces compile-time error:

Ref.java:6: error: incompatible types: RefQueue<CAP#1> cannot be 
converted to RefQueue<Object>
         RefQueue<Object> q = r.queue;
                               ^
   where CAP#1 is a fresh type-variable:
     CAP#1 extends Object super: Object from capture of ? super Object
1 error


It seems that the behaviour is inconsistent. There's also a question 
whether the compile-time error is a correct behaviour or not. I tried 
this with JDK 7u51, JDK 8 ea-b121 and recent JDK 9 from dev forest. They 
all behave the same.


Regards, Peter