Day 27-Java collections:

Collections of java:

==> Java Collections are a framework that provides a set of classes and interfaces to store and manipulate data in Java.

==> The Java Collections Framework is a part of the java.util package and is designed to handle groups of objects.

There are two main types of collections in Java:

==> Collection Interface
==> Map Interface

1.Collection Interface:

List:

==> An ordered collection that can contain duplicate elements.

ArrayList:

==> A dynamic array that grows as needed. Elements can be accessed by index.

LinkedList:

==> Doubly linked list. It allows for fast insertions/deletions at both ends but is slower for random access.

Set:

==> A collection that does not allow duplicates.

HashSet:

==> No duplicates and does not maintain any order.

LinkedHashSet:

==> No duplicates, but it maintains insertion order.

TreeSet:

==> No duplicates, and it orders elements according to their natural ordering or a comparator.

Queue:

==> A collection used for holding elements prior to processing.

PriorityQueue:

==> A queue where elements are processed in order of their priority.

LinkedList:

==> Implements both List and Queue interfaces.

2.Map Interface

==> This is not a true collection but a structure that holds key-value pairs, where each key maps to exactly one value.

HashMap:

==> A map that does not maintain any order of keys.

LinkedHashMap:

==> A map that maintains the insertion order of keys.

TreeMap:

==> A map that maintains keys in sorted order.

Example:

import java.util.*; public class CollectionExample { public static void main(String[] args) { // List Example (Allow Duplicates) List<String> list = new ArrayList<>(); list.add("Java"); list.add("Python"); list.add("Java"); System.out.println("List: " + list); // Set Example (No Duplicates) Set<String> set = new HashSet<>(); set.add("Java"); set.add("C++"); set.add("Java"); System.out.println("Set (No Duplicates): " + set); // Map Example (Key-Value pairs) Map<String, Integer> map = new HashMap<>(); map.put("Java", 8); map.put("Python", 3); map.put("JavaScript", 6); System.out.println("Map: " + map); // Queue Example Queue<String> queue = new LinkedList<>(); queue.add("First"); queue.add("Second"); queue.add("Third"); System.out.println("Queue: " + queue); } } 

Output:

List: [Java, Python, Java] Set (No Duplicates): [Java, C++] Map: {Java=8, Python=3, JavaScript=6} Queue: [First, Second, Third]