You can't, unless you know things about type T (for instance, whatever T is, the set of all unique T must be well-ordered and have an upper bound). So T must at least extend some interface that will provide this information. And if this interface provides this information, why would you need a generic class that does nothing but delegate to the methods defined in this interface?
Let's assume you want to do this as an exercise. I suggest you take a look at java.util.Collections and its min and max methods, and what their generic types are.
(Note: the "Object &" part can be omitted since every single type matches that.)