coekie / gentyref Goto Github PK

Context
Assume we have an outer class or interface A<X> with type parameters, and a static class B nested in there, which implements this or another generic class/interface C<Y> with a concrete type parameter (e.g. B implements C<String>).

class A<X> {
    static class B implements C<String> {
    }
}
interface C<Y> {}

Wrong behavior
Then GenericTypeReflector.getExactSuperType(B.class, C.class) returns the raw type C

Expected behavior
GenericTypeReflector.getExactSuperType(B.class, C.class) should return the parameterized Type C<String>.

Analysis
In GenericTypeReflector.isMissingTypeParameters (which tries to find out whether we have a (partially) raw type at hand), the loop goes through enclosing classes even if the class itself is static, and thus the type parameters of the enclosing class have no effect on the nested class. It should stop for static nested classes.

Workaround
Put your static nested class into an outer class without type parameters, or make it a top-level class itself.

Hi,

I encountered the following problem:

Given

public class Parent <A> {
  public <T extends Annotation> T getAnnotation(Class<T> clazz) {
    return null
  }
}

public class Child extends Parent<Child> {
}

this call will fail

Method m = Child.getMethod("getAnnotation", Class.class);
GenericTypeReflector.getExactReturnType(m, Child.class);

UnresolvedTypeVariableException: An exact type is requested, but the type contains a type variable that cannot be resolved.
   Variable: T from public java.lang.annotation.Annotation Parent.getAnnotation(java.lang.Class)
   Hint: This is usually caused by trying to get an exact type when a generic method who's type parameters are not given is involved.

The same call does not fail if the containing type is not parameterized.

Method m = Child.getMethod("getAnnotation", Class.class);
GenericTypeReflector.getExactReturnType(m, Class.class);

Furthermore, would it be possible to add a resolveReturnType(Method m, Object[] args) that could return the actual type for such signatures <T extends Annotation> T getAnnotation(Class<T> clazz) when the arguments are given?