Types of Collection

A Set is a collection that cannot contain duplicate elements. It is used to represent sets like the cards comprising a poker hand, the courses making up a student's schedule, or the processes running on a machine. ( HashSet, TreeSet)

A List is an ordered collection. Lists can contain duplicate elements. The user of a List generally has precise control over where in the List each element is inserted. The user can access elements by their integer index. (ArrayList, LinkedList, Vector)

 boolean add(int i, Object o); //Insert o at position i
 Object get(int i); //Return the i-th element
 Object remove(int i); //Remove the i-th elemet
 boolean set(int i, Object o); //Replace the i-th element

A Map is an object that maps keys to values. Maps cannot contain duplicate keys: Each key can map to at most one value. If you've used Hashtable(in the API reference documentation), you're already familiar with the general flavor of Map. (HashMap, TreeMap, Hashtable)

 boolean containsKey(Object key);
 boolean containsKey(Object key);
 Object get(Object key);
 Set keySet();
 Object put(Object key, Object value);
 Collection values();