Currently wildcards can only have one bound, whereas type variables can have
multiple bounds:

<T extends Number & Cloneable> void m(List<T> l);

A similar method could be expressed using wildcards with multiple bounds:

void m(List<? extends Number & Cloneable> l);

Among the benefits of using wildcards over type variables are:

1. The signature becomes simpler since you do not need to add a type variable
   to express the constraints on l.
2. The signature using wildcards states implicitly that you do not intent to
   modify l (at least not add new non-null elements).
3. It is not necessary to understand the rules of inference to read the
   signature.

###@###.### 2004-05-25