Ok - my bad. Jsut as you can raed tihs snenecte wtouiht tkiinhng
(smoe-waht), so I read the method sig. BTW, I wasn't being
condesending, just attempting to be considerate. Honestly, no bad/hard
feelings.
Anyhow, fillMap seems nice. However, would the simple
<K,V> Map<K,V> *Map(Collection<V> c, Transformer<V,K> keyTransformer)
be fillMap or toMap?
I think at least the 3 I've proposed would be handy - I personally use
LazyMaps a bit... I don't think (collection, keyTransformer,
valueTransformer) would be super necessary - can just use one more
param. Although... with generics, that could be verbose.
Also, would I be correct in assuming that HashMap is the "default" Map
implementation that people use?
Cheers
Stephen
James Carman wrote:
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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