The core collection interfaces are the foundation of the Java Collections Framework.The Java Collections Framework hierarchy consists of two distinct interface trees:
These interfaces allow collections to be manipulated independently of the details of their representation.
- The first tree starts with the
Collection
interface, which provides for the basic functionality used by all collections, such asadd
andremove
methods. Its subinterfaces Set
,List
, andQueue
provide for more specialized collections.The
Set
interface does not allow duplicate elements. This can be useful for storing collections such as a deck of cards or student records. TheSet
interface has a subinterface,SortedSet
, that provides for ordering of elements in the set.The
List
interface provides for an ordered collection, for situations in which you need precise control over where each element is inserted. You can retrieve elements from aList
by their exact position.The
Queue
interface enables additional insertion, extraction, and inspection operations. Elements in aQueue
are typically ordered in on a FIFO basis.- The second tree starts with the
Map
interface, which maps keys and values similarly to aHashtable
.
Map
's subinterface,SortedMap
, maintains its key-value pairs in ascending order or in an order specified by aComparator
.