Is lesson me hum cover karenge:

• Collection framework kya hota hai
• Collection hierarchy
• List, Set, Map kya hote hain
• Important classes (ArrayList, HashSet, HashMap)
• Real examples aur use cases

Collection framework ka matlab:

data ko store aur manage karne ke liye ready-made classes aur interfaces

Java me:

java.util package me available hota hai

Iterable
   ↓
Collection
   ├── List
   ├── Set
   └── Queue

Map (separate interface)

Example:

Collections.sort(list);

List ka use hota hai:

ordered collection + duplicate allowed

• ArrayList
• LinkedList
• Vector

import java.util.ArrayList;

class Test {

    public static void main(String[] args){

        ArrayList<Integer> list = new ArrayList<>();

        list.add(10);
        list.add(20);
        list.add(10); // duplicate allowed

        for(int n : list){
            System.out.println(n);
        }
    }
}

import java.util.LinkedList;

class Test {

    public static void main(String[] args){

        LinkedList<String> list = new LinkedList<>();

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

        System.out.println(list);
    }
}

Set ka use hota hai:

unique elements store karne ke liye

✔ duplicates allowed nahi

• HashSet
• LinkedHashSet
• TreeSet

import java.util.HashSet;

class Test {

    public static void main(String[] args){

        HashSet<Integer> set = new HashSet<>();

        set.add(10);
        set.add(20);
        set.add(10); // duplicate ignore

        System.out.println(set);
    }
}

Map ka use hota hai:

key-value pair store karne ke liye

✔ key unique hoti hai

import java.util.HashMap;

class Test {

    public static void main(String[] args){

        HashMap<String, Integer> map = new HashMap<>();

        map.put("Sujit", 90);
        map.put("Rahul", 80);

        System.out.println(map.get("Sujit"));
    }
}

for(int n : list){
    System.out.println(n);
}

Iterator<Integer> it = list.iterator();

while(it.hasNext()){
    System.out.println(it.next());
}

Collections.sort(list);
Collections.reverse(list);
Collections.max(list);

ArrayList → dynamic array
HashSet → unique data
HashMap → key-value storage (database-like)

1. Collection framework kya hota hai?
2. List aur Set me difference kya hai?
3. HashMap ka use kya hai?
4. ArrayList vs LinkedList difference?
5. Iterator kya hota hai?

Is lesson me humne seekha:

✔ Collection framework basics
✔ List, Set, Map
✔ ArrayList, HashSet, HashMap
✔ Iteration methods
✔ Real-life usage

Collection framework Java me dynamic data handling aur efficient storage ke liye use hota hai.

Java Collections Framework (JCF) is a set of classes and interfaces that provide efficient ways to store, manage, and manipulate groups of data.

• Root interface of collection hierarchy

• Common methods:

  • add()
  • remove()
  • size()
  • isEmpty()
  • contains()

• ArrayList
• LinkedList
• Vector (legacy)
• Stack (legacy)

• Maintains insertion order
• Allows duplicate elements
• Index-based access

• HashSet
• LinkedHashSet
• TreeSet

• No duplicate elements
• Uses hashing or tree structure

• PriorityQueue
• ArrayDeque

• offer()
• poll()
• peek()

• HashMap
• LinkedHashMap
• TreeMap
• Hashtable (legacy)

• Keys are unique
• Values can be duplicated

• Dynamic array
• Fast access (O(1))
• Slow insertion/deletion (O(n))

• Doubly linked list
• Fast insertion/deletion
• Slow access

• Based on hashing
• Average O(1) operations

• Sorted structure
• Based on Red-Black Tree
• O(log n) operations

• Based on Heap (Min Heap by default)
• Elements are ordered based on priority

• for loop
• enhanced for loop
• Iterator
• ListIterator
• forEach()

• Used when class defines its own sorting

• Used when we need custom sorting logic

• sort()
• reverse()
• shuffle()
• frequency()
• max()
• min()

(*peek operation)

• Hashing
• hashCode() and equals()
• Collision handling
• Load factor
• Fail-fast vs Fail-safe

• Vector
• Hashtable
• Collections.synchronizedList()
• ConcurrentHashMap

• Stream API
• Lambda Expressions
• Functional Interfaces
• Parallel Streams

• Ranking system → PriorityQueue
• Unique elements → Set
• Fast lookup → HashMap
• Sorted data → TreeSet

• Not overriding equals() and hashCode()
• Choosing wrong data structure
• Modifying collection during iteration

Java Collections Framework helps in efficient data handling using different data structures and algorithms.

This README is designed for learning, practice, and interview preparation of Java Collections Framework.