Receiver type overview

Foo.java

public class Foo<T> {

    class Bar<S> {

        Bar(Foo<T> Foo.this) {}

        void bar(Foo<T>.Bar<S> this) {}
    }

    static class Qux<S> {

        void qux(Qux<S> this) {}
    }

    void foo(Foo<T> this) {}

    static void foobar() {}
    
    static Class<?> baz() {
        class Baz<S> {
            void baz(Baz<S> this) {}
        }
        return Baz.class;
    }

    public static void main(String[] args) throws Exception {
        System.out.println(Foo.class.getDeclaredConstructor().getAnnotatedReceiverType().getType()); // class Foo
        System.out.println(Foo.class.getDeclaredMethod("foo").getAnnotatedReceiverType().getType()); // class Foo
        System.out.println(Foo.class.getDeclaredMethod("foobar").getAnnotatedReceiverType()); // null
        System.out.println(Foo.Bar.class.getDeclaredConstructor(Foo.class).getAnnotatedReceiverType().getType()); // class Foo
        System.out.println(Foo.Bar.class.getDeclaredMethod("bar").getAnnotatedReceiverType().getType()); // class Foo.Bar
        System.out.println(Foo.Qux.class.getDeclaredConstructor().getAnnotatedReceiverType().getType()); // class Foo
        System.out.println(Foo.Qux.class.getDeclaredMethod("qux").getAnnotatedReceiverType().getType()); // class Foo.Qux
        System.out.println(baz().getDeclaredConstructor().getAnnotatedReceiverType().getType()); // class Foo
        System.out.println(baz().getDeclaredMethod("baz").getAnnotatedReceiverType().getType()); // class Foo.Baz
    }
}