Collection And Map Introduction

Java Collections Hierarchy

The Collections framework is better understood with the help of core interfaces. The collections classes implement these interfaces and provide concrete functionalities.

Collection

It extends Iterable interface which adds support for iterating over collection elements using the for-each loop statement.

All other collection interfaces and classes (except Map) either extend or implement this interface. For example, List (indexed, ordered) and Set (sorted) interfaces implement this collection.

List

Some useful classes which implement List interface are – ArrayList, CopyOnWriteArrayList, LinkedList, Stack and Vector.

Set

Some useful classes which implement Set interface are – ConcurrentSkipListSet, CopyOnWriteArraySet, EnumSet, HashSet, LinkedHashSet and TreeSet.

Map

Some useful classes which implement Map interface are – ConcurrentHashMap, ConcurrentSkipListMap, EnumMap, HashMap, Hashtable, IdentityHashMap, LinkedHashMap, Properties, TreeMap and WeakHashMap.

Stack

The Java Stack interface represents a classical stack data structure, where elements can be pushed to last-in-first-out (LIFO) stack of objects. In Stack we push an element to the top of the stack, and popped off from the top of the stack again later.

Queue

Some useful classes which implement Map interface are – ArrayBlockingQueue, ArrayDeque, ConcurrentLinkedDeque, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingDeque, LinkedBlockingQueue, LinkedList, LinkedTransferQueue, PriorityBlockingQueue, PriorityQueue and SynchronousQueue.

Deque

Some common known classes implementing this interface are ArrayDeque, ConcurrentLinkedDeque, LinkedBlockingDeque and LinkedList.