Java 5, Generic, Map and wildcards

[Benjamin Lerman]

Hi all,

I've got a weird problem with generics and maps.

I have the 2 following lines :

Collection<? extends ParametresGeneraux> l = new TreeSet<ParametresGlobaux>();

Map<String,Collection<? extends ParametresGeneraux> > m = new TreeMap<String, TreeSet<ParametresGlobaux>>();

The first one causes no problem, the second one causes this error:

Type mismatch: cannot convert from TreeMap<String,TreeSet<ParametresGlobaux>> to Map<String,Collection<? extends ParametresGeneraux>>

Knowing that ParametresGlobaux extends ParametresGeneraux and TreeSet
implements Collection, I don't really see what is wrong.

Is this a misfeature of Generics, or is there any way to have this work
(other than recreating my map).

Thanks.

 

[Hendrik Maryns]

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Benjamin Lerman schreef:

Hi all,

I've got a weird problem with generics and maps.

I have the 2 following lines :

Collection<? extends ParametresGeneraux> l = new TreeSet<ParametresGlobaux>();

Map<String,Collection<? extends ParametresGeneraux> > m = new TreeMap<String, TreeSet<ParametresGlobaux>>();

Multilevel generics with wildcards are hard to understand. You want

Map<String,? extends Collection<? extends ParametresGeneraux> > m = new

The first one causes no problem, the second one causes this error:

Type mismatch: cannot convert from TreeMap<String,TreeSet<ParametresGlobaux>> to Map<String,Collection<? extends ParametresGeneraux>>

Knowing that ParametresGlobaux extends ParametresGeneraux and TreeSet
implements Collection, I don't really see what is wrong.

Is this a misfeature of Generics, or is there any way to have this work
(other than recreating my map).

See
http://www.angelikalanger.com/Gener...ments.html#What do multilevel wildcards mean?
for an excellent explanation of the matter. (or
http://tinyurl.com/h3j8y if your newsreader messes up).

HTH, H.

--
Hendrik Maryns

==================
www.lieverleven.be
http://aouw.org
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