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QueueExample.java
QueueExample.java
 
 
readme.md
readme.md
 
 

readme.md

☕ Java Lesson – Queue in Java (Collection Framework)

Is lesson me hum seekhenge:

  • Queue kya hota hai
  • FIFO concept
  • Queue interface aur implementations
  • Important methods
  • PriorityQueue vs Queue difference

1️⃣ Queue Kya Hota Hai?

Queue ek data structure hai jo follow karta hai:

FIFO (First In First Out)

Matlab:

jo element pehle aata hai, wo pehle nikalta hai

2️⃣ Real-Life Example

Line me khade log

Jo pehle line me aaya:

wo pehle service lega

3️⃣ Queue Interface

Package:

java.util.Queue

4️⃣ Queue Implementations

Java me common Queue implementations:

LinkedList
PriorityQueue
ArrayDeque

5️⃣ Basic Queue Example (LinkedList)

import java.util.*;

class Test {

    public static void main(String[] args){

        Queue<Integer> q = new LinkedList<>();

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

        System.out.println(q);

        System.out.println(q.poll()); // remove first
        System.out.println(q.peek()); // first element
    }
}

6️⃣ Important Methods

Method Use
add() element insert
offer() safe insert
poll() remove element
peek() front element
remove() remove (exception if empty)

7️⃣ add() vs offer()

Method Behavior
add() error throw karega
offer() false return karega

8️⃣ poll() vs remove()

Method Behavior
poll() null return karega
remove() exception throw karega

9️⃣ peek() vs element()

Method Behavior
peek() null return
element() exception throw

🔟 Queue with ArrayDeque

import java.util.*;

class Test {

    public static void main(String[] args){

        Queue<String> q = new ArrayDeque<>();

        q.offer("A");
        q.offer("B");
        q.offer("C");

        System.out.println(q.poll());
    }
}

1️⃣1️⃣ Queue vs PriorityQueue

Feature Queue PriorityQueue
Order FIFO Priority-based
Structure Linear Heap

1️⃣2️⃣ When to Use Queue?

Use Queue jab:

order maintain karna ho
processing sequence important ho

Example:

task scheduling
printer queue
CPU scheduling

1️⃣3️⃣ Important Points

✔ Queue interface directly instantiate nahi hota
✔ LinkedList aur ArrayDeque commonly use hote hain
✔ null values avoid karna chahiye

🎯 Interview Questions

  1. Queue kya hota hai?
  2. add() aur offer() me difference?
  3. poll() aur remove() me difference?
  4. Queue aur PriorityQueue me difference?

🧾 Lesson Summary

Is lesson me humne seekha:

✔ Queue concept (FIFO)
✔ Implementations (LinkedList, ArrayDeque)
✔ Important methods
✔ Differences aur use cases

Queue Java me sequential processing aur task management ke liye use hota hai.