Java – Collection framework

August 31, 2016 SJ Collection 0

In this article, we will discuss Collection framework in detail covering all its related interfaces and core implementation classes

1. Collection:

A collection is a group of element/objects represented as single unit/entity
On which programmers can perform various operations
Like insertion, deletion, sorting, searching, and reversing, etc.

2. Why we need Collection framework ?

In Java 1.0 version, there are several classes to achieve above mentioned concepts, but they were all arranged in ad-hoc basis
These classes are Vector, Stack, Dictionary, Hashtable and Properties
These classes collectively referred as legacy classes and every method inside legacy classes is synchronized (i.e.; Thread-safe access)
With Java 1.2 version introduction, Sun (now Oracle) group came up with Collection framework putting together above legacy classes and newly introduced classes into one place (i.e.; java.util package) under root-interface java.util.Collection

3. Advantages of Collection framework:

Used to store group of objects as a single unit/entity
Dynamically grow-able in nature i.e.; collection size increases as more number of objects added and size shrinks when deleted
Prior to Java 1.5 version introduction, collection allows to store/save any type of objects
With the introduction of generics in Java 1.5 version, collection are type-bounded (i.e.; within angle brackets, programmer can define type of objects it allows to be added)
Every collection class is based on some standard data-structures like for example, dynamic-array for ArrayList/Vector classes and hashtable for HashSet, etc
There are standard ready-made API’s available to operate on Collection like adding/deleting elements, etc
When programmer performs any operation on Collection classes, then it works based on the algorithm of the underlying data-structures
It has several interfaces/classes to operate on group of element/objects

Figure: Collection framework hierarchy

01-collection-framework-hierarchy-in-java

Source: Team BenchResources.Net

4. Core Collection interfaces:

Collection
List
Set
SortedSet
NavigableSet
Queue
Map
SortedMap
NavigableMap

5. Core Collection implementation classes:

5.1 java.util.List

ArrayList
LinkedList
Vector
Stack

5.2 java.util.Set

HashSet
LinkedHashSet
TreeSet

5.3 java.util.Queue

PriorityQueue

5.4 java.util.Map

HashMap
LinkedHashMap
IdentityHashMap
WeakHasMap
TreeMap
Hastable
Properties

Note: All core interfaces/implementation classes presents inside java.util package

6. Misconception about Map:

Although we are discussing Map under collection framework
map neither inherit any properties/methods nor implement any interfaces of collection
Since map deals with group of key-value pairs, which is represented as a single unit/entity is always discussed under collection framework

References:

Happy Coding !!
Happy Learning !!

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