try http://mindprod.com/jgloss/generics.html#SYNTATICSOUP

min1 cannot operate on collections of subtypes of T if the actual type
of T is specified explicitly.  E.g., if ActualU is a subclass of
ActualT, the compiler doesn't like min1 in this situation:

    ArrayList<ActualU> listOfU = new ArrayList<ActualU>();
    SomeClass.<ActualT>min(listOfU);
    SomeClass.<ActualT>min1(listOfU);  // No good.

Here's a more complete example:

import java.util.*;

class Main {

    public static void main(String[] args) {

         ArrayList<CU> uList = new ArrayList<CU>( );

         /* Compiler rejects min1. */
         Min.<CT>min(uList);
         Min.<CT>min1(uList);
    }

}

class CS implements Comparable<CT> {
    public int compareTo(CT ct) {
        return 0;
    }
}

class CT extends CS { }

class CU extends CT { }

class Min {
     public static <T extends Object & Comparable<? super T>>
     T min(Collection<? extends T> coll) {
        return null;
     }

     public static <T extends Object & Comparable<? super T>>
     T min1(Collection<T> coll) {
        return null;
     }
}