Java Collections Framework (JCF) for Beginners

If you're learning Java, you've probably heard about Collections. They are one of the most important concepts in Java because they help us store and manage multiple objects easily.

In this blog, let's understand Java Collections in a simple way.

** What is Java Collection?**

The Java Collections Framework (JCF) is a set of classes and interfaces that helps us store and manipulate groups of objects.

Instead of using arrays with a fixed size, collections can grow or shrink dynamically.

** Why Use Collections?**

Store multiple objects
Dynamic size
Easy to add and remove data
Built-in methods for searching and sorting
Reduces coding effort

** Collection Hierarchy**

Collection
│
├── List
│   ├── ArrayList
│   ├── LinkedList
│   └── Vector
│
├── Set
│   ├── HashSet
│   ├── LinkedHashSet
│   └── TreeSet
│
└── Queue
    └── PriorityQueue

Map (Separate Interface)
├── HashMap
├── LinkedHashMap
└── TreeMap

Note: Map is not part of the Collection interface.

** 1. List**

A List stores elements in order and allows duplicate values.

** Example**

java
import java.util.*;

public class Main {
public static void main(String[] args) {

    List<String> list = new ArrayList<>();

    list.add("Java");
    list.add("Python");
    list.add("Java");

    System.out.println(list);
}

}


**Output**

[Java, Python, Java]

** 2. Set**

A Set stores only unique elements.

java
HashSet set = new HashSet<>();

set.add("Java");
set.add("Python");
set.add("Java");

System.out.println(set);


**Output**

[Java, Python]

** 3. Queue**

A Queue follows the FIFO (First In, First Out) rule.

java
PriorityQueue queue = new PriorityQueue<>();

queue.add(30);
queue.add(10);
queue.add(20);

System.out.println(queue.poll());


**Output**


** 4. Map**

A **Map** stores data as **key-value pairs**.

``java
HashMap map = new HashMap<>();

map.put(1, "Java");
map.put(2, "Python");

System.out.println(map);
`

** Common Collection Classes**

Class	Description
ArrayList	Dynamic array
LinkedList	Fast insertion and deletion
HashSet	Stores unique elements
TreeSet	Stores unique elements in sorted order
HashMap	Stores key-value pairs
TreeMap	Stores sorted key-value pairs