Why Autoboxing did not work in Annonymous class in java

What can be the reason for this to not work?

ThreadLocal<Integer> intLocal2 = new ThreadLocal<>() {
            @Override
            protected int initialValue() { // if I use int as return type it doesn't work
                return 0;
            }
        };

but if I use Integer as return type of initialValue() it will work.

I tried this on java 11

>Solution :

Autoboxing is impossible for the return types, see the docs:
https://docs.oracle.com/javase/tutorial/java/data/autoboxing.html

Converting a primitive value (an int, for example) into an object of
the corresponding wrapper class (Integer) is called autoboxing. The
Java compiler applies autoboxing when a primitive value is:

• Passed as a parameter to a method that expects an object of the
  corresponding wrapper class.
• Assigned to a variable of the corresponding wrapper class.