First of all EnumSet/EnumMap are not general purpose collections, they are already implementation specific.
Also, since you can't subclass enum, class of contained values will be the same as declaring class. >From EnumSet documentation: "All of the elements in an enum set must come from a single enum type". I don't see how exposing getElementType() can hinder reification. I'm going to say that it doesn't. Please provide counterexample if you think I'm mistaken. Here are your use cases: 1. Remove ugly hacks from serialization libraries that were known to cause problems with different JVM implementations in the past (for example see this code from jackson: http://goo.gl/yudBps) 2. A Visual editor of some sort may display EnumSet as a list of checkboxes if it knows what type of enum values can be contained within this set. On Sat, Sep 21, 2013 at 8:15 PM, Remi Forax <fo...@univ-mlv.fr> wrote: > On 09/21/2013 05:27 PM, Marcin Wiśnicki wrote: >> >> Third party serialization libraries and other tools need to know the >> type of EnumSet elementType. Currently this field is package-private >> and said libraries have to resort to non-portable reflection hacks. >> >> Please add EnumSet#getElementType() and EnumMap#getKeyType() methods. >> >> I've submitted this request to bugs.sun.com last month, where it >> received Bug Id: 9006352. There was no further communication and that >> bug is still not visible which doesn't surprise me as I've never had >> any luck with bugs.sun.com even when submitting actual bug :( >> >> PS. Please keep me CC'ed. > > > Hi Marcin, > I've read the bug file but failed to find a description of a compelling use > case for these methods. > > Adding these two methods goes against an important rule: > try to avoid for sub-types of Collection, methods that are implementation > specific, the history has proven multiple times that implementations of > collections change a lot. This is a general rule, that we may want to ignore > but it has to worth it. > > Also, I think it worth to understand what's elementType represent. > elementType is not the class of the values contained in the set but the > declaring class (Enum.getDeclaringClass) of the enum values. So despite > being a Class, elementType is a type information that only exists has a > field because generics are not reified. This has two consequences, the first > one is that if you want to create an EnumSet, you need a way to have an > elementType and the second one is that it may make the work of the people > that want to reify generics in a future version of Java harder. > > and don't think I'm the dragon that keep the treasure, this is just my > humble opinion and I try to do my best to explain why adding these methods > is not obvious. > > regards, > Rémi > >
