Java Generic Type and Reflection

Posted by Tom Tucker on Stack Overflow See other posts from Stack Overflow or by Tom Tucker
Published on 2010-12-29T02:30:47Z Indexed on 2010/12/29 2:54 UTC
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I have some tricky generic type problem involving reflection. Here's the code.

public @interface MyConstraint {
    Class<? extends MyConstraintValidator<?>> validatedBy();
}

public interface MyConstraintValidator<T extends Annotation> {
    void initialize(T annotation);
}

/**
    @param annotation is annotated with MyConstraint.
*/
public void run(Annotation annotation) {
    Class<? extends MyConstraintValidator<? extends Annotation>> validatorClass = annotation.annotationType().getAnnotation(MyConstraint.class).validatedBy();
    validatorClass.newInstance().initialize(annotation) // will not compile!
}

The run() method above will not compile because of the following error.

The method initialize(capture#10-of ? extends Annotation) in the type MyConstraintValidator<capture#10-of ? extends Annotation> is not applicable for the arguments (Annotation)

If I remove the wild cards, then it compiles and works fine. What would be the propert way to declare the type parameter for the vairable validatorClass?

Thanks.

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