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https://issues.apache.org/jira/browse/LANG-564?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13089035#comment-13089035
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Etienne Neveu commented on LANG-564:
------------------------------------
I was also confused by the StrLookup type parameter while browsing the
commons-lang 3.0.1 source. Instead of creating a duplicate issue, I thought it
would be better to comment here, even though this issue seems to be closed...
I don't see the point of having a generic type parameter on the StrLookup
class, if it's not used anywhere. No method / field in StrLookup references
this type parameter. IntelliJ IDEA itself reports a warning: "Type parameter
'V' is never used". Moreover, Java generics are not reified, so there is no
reliable way to access the type parameter at runtime (and I don't see the point
of doing that anyway...).
While the Javadoc tries to clarify the purpose of a StrLookup, the unused type
parameter is still confusing, and the client code has to un-necessarily specify
type parameters. For example, I have to write:
{code}
StrLookup<?> lookup = StrLookup.noneLookup();
StrLookup<String> lookup2 = StrLookup.systemPropertiesLookup();
StrLookup<Integer> lookup3 = StrLookup.mapLookup(integerMap);
{code}
instead of
{code}
StrLookup lookup = StrLookup.noneLookup();
StrLookup lookup2 = StrLookup.systemPropertiesLookup();
StrLookup lookup3 = StrLookup.mapLookup(integerMap);
{code}
My best guess is that this type parameter was added when commons-lang was
generified, because StringLookup.mapLookup() takes a generified Map. Doing this
is not really needed, though: we could remove the <V> type parameter
everywhere, and replace the StrLookup.mapLookup()'s Map<String, V> with a
Map<String, ?> (which is the same as Map<String, ? extends Object>, but
shorter).
I guess it's too late to change this now, due to backward compatibility... But
I thought I'd comment just in case it's still possible.
> Improve StrLookup API documentation
> -----------------------------------
>
> Key: LANG-564
> URL: https://issues.apache.org/jira/browse/LANG-564
> Project: Commons Lang
> Issue Type: Bug
> Components: lang.text.*
> Reporter: Sebb
> Fix For: 3.0
>
>
> The API for StrLookup is confused. The class has been partly genericised, but
> why?
> The Javadoc says the class is for looking up Strings which are indexed by
> Strings, and this agrees with the method lookup()
> Surely if the class is generic on <V>, the lookup() method should return V,
> not String?
> Does it make any sense for the class to return anything but a String? If not,
> then why is the class generic?
> If it does make sense, then lookup() should return V.
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