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https://issues.apache.org/jira/browse/COLLECTIONS-519?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13986550#comment-13986550
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Sebb commented on COLLECTIONS-519:
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I still think it would have been better to extend the existing utility class by
composition rather than sub-classing.
1) the sub-class does not prevent access to the underlying static methods. It
would be easy to accidentally invoke the wrong method.
2) If a new method is added to the Collections class, it will be automatically
made available to the derived class. This can cause problems if the derived
class happens to have chosen the same method signature for different
functionality.
It can also cause issues if the new method is a sibling to an existing method
that is deliberately hidden in the derived class; the user would then be able
to bypass the local class.
Allowing subclassing of utuility classes does make life simpler for the
developer, but only initially.
However, it does not provide safety for the user of the subclass, and I suspect
it will cause additional headaches for the developer in the long term.
I agree with @Dipanjan Laha that this is not a valid use case for extension; so
yes the utilty class should be regarded as final
> private constructors in utility classes break existing code
> -----------------------------------------------------------
>
> Key: COLLECTIONS-519
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-519
> Project: Commons Collections
> Issue Type: Bug
> Affects Versions: 4.x
> Reporter: Radoslav Paskalev
> Fix For: 4.1
>
>
> Hello,
> In collections version 4.x all utility classes (example ListUtils, MapUtils,
> PredicateUtils....) have private constructors. I consider this to be a
> serious bug, as it breaks any possibility the classes to be extended by the
> users. The javadoc says that constructors are private in order to prevent
> class instantiation but this object instantiation is not really problem and i
> think it is more important to allow classes to be extended. The possibility
> to extend utility classes was one of the major selling points of commons.lang
> and commons.collections projects. In the latest commons.lang project the
> utility classes still have public constructors.
> Best Regards
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