raw types warnings and instanceof

Maurizio Cimadamore Maurizio.Cimadamore at Sun.COM
Mon Nov 3 04:14:35 PST 2008

I've just started  a poll on my blog; should you find other weird cases 
of raw warnings incorrectly (or I should say redundantly) being 
generated by javac - please post them in my blog. Here's the URL:


Currently on the list:

*) Remove raw warnings for cast/instanceof
*) Add special case for Class<RAWTYPE>

Thanks to everyone for all the comments on this issue and for your 
effort in making javac a better compiler.

Maurizio Cimadamore wrote:
> Hi
> FYI here's the warning I found when cleaning up langtools; as I said 
> there are only two warnings that cannot be fixed - both of the same 
> kind; both warnings are generated by the following code pattern:
> Class<?> token;
> Object value = Enum.valueOf((Class)token, "");
> Since Enum.valueof is a generic method declaring an fbound (<T extends 
> Enum<T>>) , it's not possible to find an instantiation for the 
> type-parameter T without going through an unchecked method call. In 
> fact, all possible kinds of checked call will result in a compile-time 
> error. The only way to remove this warning is to have some type that 
> could be used for parameterizing  the 'Class' in the cast.
> Class<?> token;
> Object value = Enum.valueOf((Class<T>)token, '');
> The problem is that, obviously, we don't always have such a T so that 
> this warning could be unavoidable.
> Maurizio
> Rémi Forax wrote:
>> Martin Buchholz a écrit :
>>> Here's another case where raw type warnings seem
>>> well-intentioned, but going too far.
>>>  $ cat ClassRaw.java; jver coll jr ClassRaw
>>> public class ClassRaw {
>>>     public static void main(String[] args) throws Throwable {
>>>         Class<Comparable> x = Comparable.class;
>>>     }
>>> }
>>> ==> javac -Xlint:all ClassRaw.java
>>> ClassRaw.java:3: warning: [raw-type] found raw type: 
>>> java.lang.Comparable
>>> missing type parameters for generic class java.lang.Comparable<T>
>>>         Class<Comparable> x = Comparable.class;
>>>               ^
>>> 1 warning
>>> My first impression is that these warnings are more verbose,
>>> more annoying, and less likely to find bugs than even "unchecked",
>>> and that even pedants like myself will change their scripts to do
>>> -Xlint:all,-rawtypes instead of -Xlint:all
>>> Martin
>> The problem with  Class<Comparable> is that it's a rare type, a mix 
>> between parameterized type
>> and raw type and you clearly want to detect them, by example a use of 
>> List<List>> should raise a warning.
>> In my opinion, there is two way to solve the problem:
>> 1) change the JLS to use wildcard instead of raw type in getClass() 
>> and .class,
>>     this require to add an unsafe conversion between a rare type and 
>> its equivalent using a wildcard
>>     to avoid to emit an error in code that compile with prevous version.
>> 2) Have a special rule for Class<>, i.e allow Class of a raw type 
>> without emitting any warning.
>> Rémi

More information about the compiler-dev mailing list