The ParameterizedType implementation returned by getGenericParameterTypes does not override toString, so printing out one these beasts yields no useful information. The following program illustrates the problem:

import java.util.*;
import java.lang.reflect.*;

public class Junk {
    public static void main(String[] args) throws Exception {
        System.out.println(Junk.class.getMethod("foo", List.class).
                           getGenericParameterTypes()[0]);
    }

    public void foo(List<String> dogs) {}
}

Running this program prints:

sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl@1a758cb