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http://issues.apache.org/jira/browse/COLLECTIONS-110?page=comments#action_12413907
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Sergei Ivanov commented on COLLECTIONS-110:
-------------------------------------------
[cross-posted from Bugzilla]
------- Additional Comment #6 From Sergei S. Ivanov 2006-05-22 21:49 [reply]
-------
(In reply to comment #4)
> The project was done without good technical knowledge of Java 1.5
parametized
> classes.
> THE TYPICAL ERROR:
> class Set<E> {
> void add(E d) {...} // that's wrong!!!
> }
> - the method add should read
> void add(<? extends E> d) {...} // so any subclass of E is acceptable.
I am sorry to disappoint you, but the code above is not wrong. add(E) will
accept any subclass of actual type argument. The example below is fully
legitimate:
Set<Number> set = new HashSet<Number>();
set.add(new Double(0));
Please have a look, how Set<E> interface is defined in the JDK.
As for the wildcards (? extends/super E), they are mostly needed, when you
have generic objects being passed into/returned from methods. Remember that
you cannot pass object, which is declared as Set<Double>, to a function that
accepts a Set<Number> as an argument, but you can do it if the argument type
is declared as Set<? extends Number>.
Without any aim to offend you, I would strongly recommend you revisiting the
tutorial you mentioned.
> [collections] Support parametized classes with commons.collections.
> -------------------------------------------------------------------
>
> Key: COLLECTIONS-110
> URL: http://issues.apache.org/jira/browse/COLLECTIONS-110
> Project: Commons Collections
> Type: Bug
> Environment: Operating System: other
> Platform: Other
> Reporter: Colbert Philippe
>
> It's time to create a parallel version of commons.collections to support
> parametized classes of each container class and abstract class. It's not
> that
> hard. There is a 23 PDF document on Sun Java website describing in detail
> how
> it should be done and what to watch out for.
> I already converted a few classes from commons.collection privately for my
> own
> needs. Once you get the hang of it, it's a rather quick process.
> I am even willing to volunteer my time to do some more but I need the
> collaboration of some of the original programmers to watch over things.
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