// Funktionen
public static <T1,T2> List<T2> map(UnaryOp<T1,T2> obj,List<T1> l) 
    {
        // Determine the dynamic type of the list
        Class<? extends List> c = l.getClass();
        try {
            // Create a result list of the same List type
            List<T2> result = c.newInstance();
            //type.cast(type.newInstance());
            // Copy elements satifying p
            for ( T1 x : l )
                result.add(obj.op(x));
            return result;   
        }
        catch (Exception e) {
            return null;
        }
    }

public interface UnaryOp<T,U> {
    U op(T x);
}

public class Sign implements UnaryOp<Integer,Integer> {
    public Integer op(Integer x) {
        return x.compareTo(0);
    }
}