java collection:
Under the java.util.* package, three commonly used interfaces are defined:
The java.util.Set interface and its subclasses: set provides no collection;
The java.util.List interface and its subclasses: List provides an ordered collection;
The java.util.Map interface and its subclasses: Map provides a collection data structure with a mapping relationship.
Collection interface:
List：ArrayList，LinkedList，Vector
Set：HashSet，TreeSet
Map interface:
HashMap，HashTable
Iterator: Iterator cooperates with list and set to perform set operations.
Collection framework: a set of class libraries for data structures implemented in java;
Three major interfaces: List, Set, Map