Figure 6: The Collection interface

Interface Collection
{
   // All mutators are optional!
   boolean      add(Object o);
   boolean      addAll(Collection c);
   void         clear();
   boolean      contains(Object o);
   boolean      containsAll(Collection c);
   boolean      equals(Object o);
   int          hashCode();
   boolean      isEmpty();
   Iterator     iterator();
   boolean      remove(Object o);
   boolean      removeAll(Collection c);
   boolean      retainAll(Collection c);
   int          size();
   Object[]     toArray();
   Object[]     toArray(Object[] a);
}