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From Dipanjan Laha <dipanja...@gmail.com>
Subject Re: [collections] Issues with MultiMap generics and need of a MultiTrie
Date Sun, 02 Mar 2014 17:06:11 GMT
Hi Matt,

Thanks for the info. I have a Jira issue created for this (
https://issues.apache.org/jira/browse/COLLECTIONS-508). I have attached the
patch there.

Thanks
Dipanjan


On Sun, Mar 2, 2014 at 10:21 PM, Matt Benson <gudnabrsam@gmail.com> wrote:

> Apache lists generally don't allow attachments. Please raise a JIRA issue
> and attach there.
>
> Matt
>
>
> On Sun, Mar 2, 2014 at 10:46 AM, Dipanjan Laha <dipanjan21@gmail.com>
> wrote:
>
> > Hi Thomas,
> >
> > I have implemented the MultiValuedMap interface, the MultiValuedHashMap
> > and a MultiValuedHashMapTest as per the discussions. I haven't completed
> > the documentation yet. If the implementations look fine, I will add the
> > remaining documentations.
> >
> > A few more points regarding the implementation
> >
> > 1. I have added a few methods to the MultiValuedMap interface which were
> > not there in the MultiMap. I think they would be a good addition to the
> > interface IMHO. They are
> >     boolean containsValue(Object key, Object value);
> >     int totalSize();
> >     void putAll(MultiValuedMap<? extends K, ? extends V> map);
> > 2. I have added an AbstractMultiValuedMapDecoractor on the lines
> > of AbstractMapDecorator, which can be extended by other MultiValuedMap
> > implementations like say a MultiValuedTreeMap
> > 3. I have created MultiValuedGet and MultiValuedPut to honor the Get/Put
> > split concepts. It was not possible for MultiValuedMap to extend the Get
> &
> > Put directly due to the limitations I had mentioned in my earlier mail.
> > 4. I have marked the incomplete documentations with TODO tags.
> >
> > PFA the patch for the new Classes. Please go through the implementation
> > and let me know if I missed some thing or if things need to be done in
> some
> > other way.
> >
> > Regards
> > Dipanjan
> >
> >
> >
> > On Wed, Feb 26, 2014 at 8:04 PM, Dipanjan Laha <dipanjan21@gmail.com
> >wrote:
> >
> >> Thanks for pointing this out. However, implementing Get & Put directly
> >> would pose the following problems.
> >>
> >> If interface MultiValuedMap<K,V> extends Get<K,Collection<V>>
> >>
> >> the method "values" would be forced to have a signature of
> >>
> >> Collection<Collection<V>> values()
> >>
> >> whereas we would want
> >>
> >> Collection<V> values().
> >>
> >> This wont be possible as we would extend Get with the generics
> >> <K,Collection<V>> as we want the method "get" to have a signature
like
> >>
> >> Collection<V> get(Object key)
> >>
> >> Now, extending the Put interface with generics <K,V> does not pose that
> >> much of an issue except that the Map interface in Java 7 has a put
> >> signature as V put(K key, V value)  whereas the Collections 4 Put still
> has
> >> Object put(Key k, V value), but we can ignore this if we want.
> >>
> >> For the problem with Get, we can have a parallel MultiValuedGet and
> >> MultiValuedPut interfaces to honor the Get/Put split concepts. Although
> we
> >> don't really need the MultiValuedPut, we can have that for consistency.
> >>
> >> Let me know your thoughts on this.
> >>
> >> Regards
> >> Dipanjan
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> On Wed, Feb 26, 2014 at 7:12 PM, Matt Benson <gudnabrsam@gmail.com
> >wrote:
> >>
> >>> Don't forget about the Get/Put/split map concepts from Collections 4.
> It
> >>> would seem you could implement those interfaces and provide that amount
> >>> of
> >>> abstraction anyway.
> >>>
> >>> Matt
> >>> On Feb 26, 2014 3:26 AM, "Dipanjan Laha" <dipanjan21@gmail.com> wrote:
> >>>
> >>> > Hi Thomas,
> >>> >
> >>> > This sounds great. Moving MultiKeyMap to the new package does sound
> >>> like
> >>> > the way to go ahead. I will start with the implementation of the
> >>> interface
> >>> > and the MultiValuedHashMap. I should be able to submit a patch with
a
> >>> basic
> >>> > implementation and some test cases by the end of this week. I can
> then
> >>> > modify and incorporate changes as per your review and suggestions.
> >>> >
> >>> > Regards
> >>> > Dipanjan
> >>> >
> >>> >
> >>> > On Wed, Feb 26, 2014 at 2:32 PM, Thomas Neidhart
> >>> > <thomas.neidhart@gmail.com>wrote:
> >>> >
> >>> > > Hi Dipanjan,
> >>> > >
> >>> > > I was thinking about a name for the new interface, but I actually
> >>> like
> >>> > your
> >>> > > proposal of MultiValuedMap.
> >>> > >
> >>> > > For the package, I think we can stick with multimap, and at some
> >>> point we
> >>> > > could also move the MultiKeyMap there, which would be logical
imho.
> >>> > >
> >>> > > The implementation names are also sound.
> >>> > >
> >>> > > Thomas
> >>> > >
> >>> > >
> >>> > >
> >>> > >
> >>> > > On Wed, Feb 26, 2014 at 9:28 AM, Dipanjan Laha <
> dipanjan21@gmail.com
> >>> >
> >>> > > wrote:
> >>> > >
> >>> > > > Hi Thomas,
> >>> > > >
> >>> > > > It would be great if we can start the discussion on the new
> >>> interface
> >>> > for
> >>> > > > MultiMap and a new package for the implementations as suggested
> by
> >>> you.
> >>> > > > Then I'll be able to put some code together for the same.
> >>> > > >
> >>> > > > IMO we can have
> >>> > > >
> >>> > > > 1. New Interface for MultiMap with the name MultiValuedMap
or
> >>> > MultiValMap
> >>> > > >  (as MultiValueMap is already the existing implementing class).
> >>> > > > 2. New package for the implementations:
> >>> > > > org.apache.commons.collections.multimap or
> >>> > > > org.apache.commons.collections.multivaluedmap
> >>> > > > 3. Implementation names like : MultiValuedHashMap,
> >>> MultiValuedTreeMap
> >>> > etc
> >>> > > >
> >>> > > > Please let me know of your thoughts on these.
> >>> > > >
> >>> > > > Regards
> >>> > > > Dipanjan
> >>> > > >
> >>> > > > On Sun, Feb 23, 2014 at 8:36 PM, Dipanjan Laha <
> >>> dipanjan21@gmail.com>
> >>> > > > wrote:
> >>> > > >
> >>> > > > > Hi Thomas,
> >>> > > > >
> >>> > > > > Thanks for your feedback. I created an improvement request
in
> >>> Jira
> >>> > for
> >>> > > > the
> >>> > > > > same (https://issues.apache.org/jira/browse/COLLECTIONS-508
)
> >>> as I
> >>> > > > > thought it could be better tracked there. Sorry for
the
> >>> duplication
> >>> > in
> >>> > > > the
> >>> > > > > mail list and Jira. I have also attached a patch in
Jira where
> I
> >>> have
> >>> > > > > modified the existing MultiMap interface and the MultiValueMap
> >>> > > > > implementation and their test cases. I agree that it
would
> break
> >>> > > backward
> >>> > > > > compatibility and we should go with your suggestion
of
> >>> deprecating
> >>> > the
> >>> > > > > existing ones and design fresh interfaces for the same.
The
> >>> patch is
> >>> > > > just a
> >>> > > > > sample implementation to demonstrate the issue and is
far from
> >>> being
> >>> > > > > complete in terms of documentation and test cases. I
am also
> >>> > attaching
> >>> > > > the
> >>> > > > > patch here for your reference.
> >>> > > > >
> >>> > > > > Please go through the patch and also let me know of
your
> >>> thoughts on
> >>> > > how
> >>> > > > > we should proceed with the new interface and package
structure.
> >>> I'll
> >>> > be
> >>> > > > > happy to change and redirect the implementation as per
your
> >>> > > suggestion. I
> >>> > > > > am new to Apache Commons, but with some guidance I should
not
> >>> have
> >>> > > issues
> >>> > > > > implementing them to start with.
> >>> > > > >
> >>> > > > > As for MultiTrie, as you mentioned, we can start with
it once
> >>> the new
> >>> > > > > MultiMap has been finalized.
> >>> > > > >
> >>> > > > > Regards
> >>> > > > > Dipanjan
> >>> > > > >
> >>> > > > >
> >>> > > > >
> >>> > > > >
> >>> > > > > On Sun, Feb 23, 2014 at 6:09 PM, Thomas Neidhart <
> >>> > > > > thomas.neidhart@gmail.com> wrote:
> >>> > > > >
> >>> > > > >> On 02/22/2014 02:00 PM, Dipanjan Laha wrote:
> >>> > > > >> > Hello,
> >>> > > > >>
> >>> > > > >> Hi Dipanjan,
> >>> > > > >>
> >>> > > > >> > Recently I had the need of using a MultiMap
in one of my
> >>> > projects. I
> >>> > > > >> found
> >>> > > > >> > that commons collection already has a MultiMap
interface and
> >>> an
> >>> > > > >> > implementation.
> >>> > > > >> >
> >>> > > > >> > While using the same, I found that the MultiMap
interface
>  has
> >>> > > methods
> >>> > > > >> that
> >>> > > > >> > are not strongly typed even though the interface
supports
> >>> > generics.
> >>> > > > For
> >>> > > > >> > example if I have a MultiMap like so
> >>> > > > >> >
> >>> > > > >> > MultiMap<String, User> multiMap = new
MultiValueMap<String,
> >>> > User>();
> >>> > > > >> >
> >>> > > > >> > where User is a custom  Class, then the get(key)
method
> would
> >>> > return
> >>> > > > me
> >>> > > > >> an
> >>> > > > >> > Object which I would need to cast to a Collection
like so
> >>> > > > >> >
> >>> > > > >> > Collection<User> userCol = (Collection<User>)
> >>> multiMap.get(key);
> >>> > > > >> >
> >>> > > > >> > I understand that this limitation comes from
that fact that
> >>> the
> >>> > > > MultiMap
> >>> > > > >> > extends IterableMap which in turn extends Map
and other
> >>> > interfaces.
> >>> > > > >> Hence
> >>> > > > >> > the MultiMap cannot have a get method which
returns a
> >>> Collection
> >>> > > > >> instead of
> >>> > > > >> > Object as that would mean extending IterableMap
with the
> >>> Generics
> >>> > > set
> >>> > > > >> to be
> >>> > > > >> > <K,Collection<V>>. In that case
the put method's signature
> >>> would
> >>> > > > become
> >>> > > > >> >
> >>> > > > >> > public Collection<V> put(K key, Collection<V>
value);
> >>> > > > >> >
> >>> > > > >> > which we do not want.The same problem would
arise with other
> >>> > methods
> >>> > > > as
> >>> > > > >> > well, ex: containsValue method.
> >>> > > > >> >
> >>> > > > >> > My proposal is why carry on the signatures
of a Map and put
> >>> it on
> >>> > > > >> MultiMap.
> >>> > > > >> > Where as I do agree that it is a Map after
all and has very
> >>> > similar
> >>> > > > >> > implementation and functionality, it is very
different at
> >>> other
> >>> > > > levels.
> >>> > > > >> And
> >>> > > > >> > even though the MultiMap interface supports
generics, the
> >>> methods
> >>> > > are
> >>> > > > >> not
> >>> > > > >> > strongly typed, which defeats the purpose of
having
> generics.
> >>> So
> >>> > why
> >>> > > > >> can't
> >>> > > > >> > we have a separate set of interfaces for MultiMap
which do
> not
> >>> > > extend
> >>> > > > >> Map.
> >>> > > > >> > That way we can have strongly typed methods
on the MultiMap.
> >>> > > > >>
> >>> > > > >> The MultiMap interface as it is right now is flawed,
and
> should
> >>> have
> >>> > > > >> been cleaned up prior to the 4.0 release imho (and
I regretted
> >>> it
> >>> > > > >> already before your post).
> >>> > > > >>
> >>> > > > >> As you correctly pointed out, the problem comes
from the fact
> >>> that
> >>> > it
> >>> > > > >> extends Map<K, Object> which leads to problems
once generics
> >>> have
> >>> > been
> >>> > > > >> introduced (before it did not matter that much as
you had to
> >>> cast
> >>> > > > >> anyway, as it is also documented in the javadoc).
> >>> > > > >>
> >>> > > > >> One mitigation for this was the introduction of
this method to
> >>> > > > >> MultiValueMap, but it is clearly not enough:
> >>> > > > >>
> >>> > > > >>  public Collection<V> getCollection(Object
key)
> >>> > > > >>
> >>> > > > >>
> >>> > > > >> Unfortunately, it is not easy to fix this now after
> collections
> >>> 4.0
> >>> > > has
> >>> > > > >> been released. We need to keep backwards compatibility,
but we
> >>> could
> >>> > > do
> >>> > > > >> the following:
> >>> > > > >>
> >>> > > > >>  * deprecate the existing interfaces/classes:
> >>> > > > >>    - MultiMap
> >>> > > > >>    - MultiValueMap
> >>> > > > >>
> >>> > > > >>  * design a new, clean interface (by not extending
Map)
> >>> > > > >>  * add new package multimap with concrete implementations
for
> >>> > > different
> >>> > > > >>    types of maps (right now only hashmaps are supported)
> >>> > > > >>
> >>> > > > >> > Please let me know your thoughts on this. I
can submit a
> >>> patch for
> >>> > > > these
> >>> > > > >> > changes based on your feedback. One more thing,
I also am in
> >>> need
> >>> > > of a
> >>> > > > >> > MultiTrie which is currently not there. I am
implementing
> the
> >>> same
> >>> > > by
> >>> > > > >> > wrapping PatriciaTrie. Now I am a bit confused
here as, if I
> >>> make
> >>> > > the
> >>> > > > >> > MultiTrie interface on the lines of MultiMap,
it would have
> >>> the
> >>> > same
> >>> > > > >> > limitations. In that case I was planning to
have a separate
> >>> set of
> >>> > > > >> > interfaces for MultiTrie which does not extend
any other
> >>> > interface.
> >>> > > > And
> >>> > > > >> in
> >>> > > > >> > case, we do change the MultiMap interface to
be independent
> of
> >>> > Map,
> >>> > > > then
> >>> > > > >> > MultiTrie can extend MultiMap. Please let me
know your
> >>> thoughts on
> >>> > > > this
> >>> > > > >> as
> >>> > > > >> > well as I am implementing the same for my project
right now
> >>> and
> >>> > > would
> >>> > > > >> like
> >>> > > > >> > to contribute it back to the commons collection.
> >>> > > > >>
> >>> > > > >> Patches are always welcome, but we first need a
decision in
> >>> which
> >>> > > > >> direction to go, see above.
> >>> > > > >>
> >>> > > > >> Regarding the MultiTrie:
> >>> > > > >>
> >>> > > > >> Indeed, it is the same problem, so it should go
hand in hand
> >>> with
> >>> > the
> >>> > > > >> revamp of the MultiMap interface.
> >>> > > > >>
> >>> > > > >> Thomas
> >>> > > > >>
> >>> > > > >>
> >>> > ---------------------------------------------------------------------
> >>> > > > >> To unsubscribe, e-mail: dev-unsubscribe@commons.apache.org
> >>> > > > >> For additional commands, e-mail: dev-help@commons.apache.org
> >>> > > > >>
> >>> > > > >>
> >>> > > > >
> >>> > > >
> >>> > >
> >>> >
> >>>
> >>
> >>
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: dev-unsubscribe@commons.apache.org
> > For additional commands, e-mail: dev-help@commons.apache.org
> >
>

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