Collections in Java

what is collection in java?

• A Collection in Java is like a container that is used to store a group of objects together and perform operations like adding, removing, searching, and sorting easily.
• It is part of the Java Collection Framework in the java.util package.

Key Points:

• Present in java.util package.

• Dynamic size → can grow or shrink.

• Built-in methods → add, remove, search, sort, etc.

• Supports interfaces: List, Set, Queue, Map.

Main Parts of the Java Collection Framework:

• Interface
• Implementation class
• Algorithms
• Iterators

1. Interfaces:

They provide the blueprint for collections.

Main interfaces:

Collection (root interface)

List → Ordered, allows duplicates

Set → No duplicates

Queue → FIFO (First In First Out)

Map (separate, stores Key–Value pairs)

2. Implementations (Classes):

These are the actual classes that implement the interfaces.

Interface Common Classes

List - ArrayList, LinkedList, Vector, Stack

Set - HashSet, LinkedHashSet, TreeSet

Queue - PriorityQueue, LinkedList, ArrayDeque

Map - HashMap, LinkedHashMap, TreeMap, Hashtable

3. Algorithms:

Utility methods provided by the Collections class:

• Sorting → Collections.sort(list)

• Searching → Collections.binarySearch(list, key)

• Shuffling → Collections.shuffle(list)

• Reverse → Collections.reverse(list)

4. Iterators:

Used to traverse elements in a collection:

• Iterator → Basic iterator, forward direction.

• ListIterator → Forward & backward traversal.

• Enumeration → Legacy iterator for older collections.