Btw. the API previously was like this:

    public <T extends Annotation> List<Class<? extends ConstraintValidator<T, ?>>> getConstraintValidatorDefinition(
        Class<T> annotationClass) { ... }

    public <A extends Annotation> void addConstraintValidatorDefinition(
        Class<A> annotationClass, 
        List<Class<? extends ConstraintValidator<? extends Annotation, ?>>> definitionClasses) {...}

So IMO it's not really more type variables, but the API is more consistent now, as it uses the same type restrictions for put and get.