Hi Stephen,
I've never thought of using a Transformer, it seems like a better way of
doing it without the need to add new bloat to the collections package.
I've put my class and test on to JIRA COLLECTIONS-263 if you want to
take a look. I'm not sure if it will sort faster than the transformer
method you have shown, there is a load test method in my test on JIRA.
regards,
John.
Stephen Kestle 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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