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https://issues.apache.org/jira/browse/WICKET-5350?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14076410#comment-14076410
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Carl-Eric Menzel commented on WICKET-5350:
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Wildcards make collections read-only. You cannot add anything to a List<?
extends Person>, because it might be a List<Employee>. You couldn't add a
Manager to it then, nor could you add an Employee to a List<Manager>.
It's especially annoying in the Model.of... case. You have a List<Person>, you
use Model.ofList and you get back an IModel<List<? extends Person>> which is
confusing and means you can't do this anymore: model.getObject().add(myPerson).
It's read-only. So if you have a list of something, you can't just give it as a
model to a choice component by calling Model.of.
In my opinion wildcards should be avoided unless there is a very good reason to
use them.
> Enhancement for AbstractChoice and WildcardListModel API
> --------------------------------------------------------
>
> Key: WICKET-5350
> URL: https://issues.apache.org/jira/browse/WICKET-5350
> Project: Wicket
> Issue Type: Improvement
> Affects Versions: 6.10.0, 7.0.0-M1
> Reporter: Betlista
> Assignee: Sven Meier
> Priority: Minor
> Labels: generics
>
> According to Efective Java book
> (http://devender.files.wordpress.com/2008/05/effectivejava.pdf), item 28:
> "No wildcard type for return value"
> Especially "User should not have to think about wildcards to use your API".
> so
> public List<? extends E> getChoices()
> should be changed to
> public List<E> getChoices()
> and for WildcardListModel
> protected List<? extends T> createSerializableVersionOf(List<? extends T>
> object)
> should be changed to
> protected List<T> createSerializableVersionOf(List<? extends T> object)
> Probably there is a lot of such things in framework.
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