The method MethodHandleNatives.getMethodName:
      static MemberName getMethodName(MethodHandle self) { ... }

takes a method handle and returns a MemberName describing it. A MemberName should encode enough information to nominally recreate the method handle via Lookup.find{Virtual,Static,Constructor}, LDC, or reflection.

If you create a method handle with Lookup.findConstructor:
    MethodHandle mh = MethodHandles.lookup().findConstructor(String.class,
                          MethodType.methodType(void.class, char[].class));
    MemberName mn = MethodHandleNatives.getMethodName(mh);

you would expect the following results:
  mn.getName() => <init>
  mn.getDeclaringClass() => String.class
  mh.getMethodType() => (char[])String or (char[])V
  mh.isConstructor => true

Instead, you get the following results:

  mn.getName() => identity
  mn.getDeclaringClass() => com.sun.invoke.util.ValueConversions
  mh.getMethodType() => (Object)Object
  mh.isConstructor => false