Brief introduction
java.util.Set java.util.List interfaces and interfaces, same as inherited from the Collection interface, its methods and the Collection interface are basically the same, and no expansion of the Collection interface function, but more stringent than the Collection interface. The difference is that with the List interface,
the Set interface elements of disorder, and some rules will ensure non-duplication into the elements.
Set of elements extracted set manner may be employed: iterator, for enhanced