Mr. Kestle,
"Map<C, K,V> CollectionUtils.toMap(Collection<C> input,
Transformer<C,K> keyTransformer, Transformer<C,V> valueTransformer,
Map<K,V> map)"
I wouldn't usually reply, in the hopes that you put your code through
a compiler and apologize for being condescending all by yourself,
but...
What I think you meant to type was (with <C,K,V> being the type
variables of the method itself):
<C,K,V> Map<K,V> CollectionUtils.toMap(Collection<C> input,
Transformer<C,K> keyTransformer, Transformer<C,V> valueTransformer,
Map<K,V> map);
So, the actual method might look like:
public static <C,K,V> Map<K,V> toMap(Collection<C> input,
Transformer<C,K> keyTransformer,
Transformer<C,V> valueTransformer,
Map<K,V> map)
{
for (C c : input)
{
map.put(keyTransformer.transform(c), valueTransformer.transform(c));
}
return map;
}
If you put "Map<C,K,V>" in your code, the compiler will complain with
the error message "wrong number of type arguments; required 2."
I might also change the method's name to "fillMap" rather than "toMap"
as it seems more descriptive of what you're doing. If it were toMap,
I wouldn't expect the input map to be there at all. The transformer
type parameters would give you enough type safety and you could just
instantiate a HashMap or something to return it.
On 9/2/07, Stephen Kestle <[EMAIL PROTECTED]> wrote:
> I wouldn't usually reply, in the hopes that you re-read the method
> signature...
> C is the input collection
> K,V are the usual types for map
> There are two transformers Transformer<C,K> and Transformer<C,V> that
> transform the collection input type to the respective map key, value types.
>
> The second signature only has <K,V> as there is no value transformer, so
> the input collection is the type of value.
>
> Cheers
>
> Stephen
>
> James Carman wrote:
> > What is "Map<C,K,V>" here? The Map interface only has two type
> > parameters, right? Shouldn't it just be Map<K,V>?
> >
> > On 8/29/07, *Stephen Kestle * <[EMAIL PROTECTED]
> > <mailto:[EMAIL PROTECTED]>> wrote:
> >
> > Hi John,
> >
> > I have not opened a ticket yet, but ... I have had very similar
> > requirements, and will [most-likely] be putting something in that
> > will solve your problem.
> >
> > However, it will not be a class - consider this method
> >
> > Map<C, K,V> CollectionUtils.toMap(Collection<C> input,
> > Transformer<C,K> keyTransformer, Transformer<C,V>
> > valueTransformer, Map<K,V> map)
> >
> > You could then do what you wanted, passing in your integer
> > transformer for the key, and potentially MultiHashMap for the map.
> >
> > NB - this is in an ideal (and we're heading to that) collections
> > world. MultiHashMap will need to be changed to extend map
> > properly and implement the interface in a consistent way (not
> > breaking Map contract etc).
> >
> > Also note that there will be other variations on the method - most
> > commonly
> >
> > Map<K,V> CollectionUtils.toMap(Collection<V> input,
> > Transformer<V,K> keyTransformer){
> > return toMap(input, keyTransformer, NOPTransformer, new
> > HashMap<K,V>());
> > }
> >
> > I'll raise a ticket within the next few days - watch this list!
> >
> > Cheers
> >
> > Stephen
> >
> > John wrote:
> >> Hi,
> >>
> >> I'm new to the collections mailing list and I have a class I
> >> think would be appropriate to be donated to the collections API.
> >>
> >> This is an extension of the MultiHashMap and filters a given
> >> Collection by a given field. It will put the objects into the map
> >> using the field value as the key.
> >>
> >> For example, lets say I have a class X which has an integer i. I
> >> have four instances of X each with the following names and values
> >> of i.
> >>
> >> x1 i=1
> >> x2 i=2
> >> x3 i=2
> >> x4 i=5
> >>
> >> The resulting MultiHashMap will contain the following after a
> >> call to
> >> sortCollection(X.class, "i"); has been made.
> >>
> >> key | Objects
> >> 1 | x1
> >> 2 | x2, x3
> >> 5 | x4
> >>
> >> I can then get a Collection of sorted objects by asking the map
> >> for the key value. I find this very useful in many situations I
> >> have come across. I will of course make the required doc, package
> >> and src formatting changes to the class before submitting it.
> >>
> >> Please can you take a look and tell me if it is worth committing
> >> this to the Collections repository. What is the process I need to
> >> go through before committing? I'm a bit pressed for time at the
> >> mo' so I can't really spend too much time working on the
> >> Collections API as a regular developer. I am a big fan of the
> >> commons Collections API and commons project in general, just wish
> >> I had more time to get involved.
> >>
> >> Kind regards,
> >>
> >> John Hunsley.
> >> Technical Supervisor, Cy-nap Ltd.
> >>
> >> ------------------------------------------------------------------------
> >>
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> >
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> >
> >
> >
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>
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