SE450: Horstmann Chapter 7: Wildcards

Typical example--start with

public static <E extends Comparable<E>> E getMax(ArrayList<E> a)
{
   E max = a.get(0);
   for (int i = 1; i < a.size(); i++)
      if (a.get(i).compareTo(max) > 0) max = a.get(i);
   return max;
}

E extends Comparable<E> so that we can call compareTo
Too restrictive--can't call with ArrayList<GregorianCalendar>
GregorianCalendar does not implement Comparable<GregorianCalendar>, only Comparable<Calendar>

Wildcards to the rescue:

public static <E extends Comparable<? super E>> E getMax(ArrayList<E> a)