Skip to content

PriorityQueue

Directory actions

More options

Directory actions

More options

Latest commit

 

History

History

PriorityQueue

Folders and files

NameName
Last commit message
Last commit date

parent directory

..
PriorityQueueTest.java
PriorityQueueTest.java
 
 
readme.md
readme.md
 
 

readme.md

☕ Java Lesson – Priority Queue in Java

Is lesson me hum seekhenge:

  • Priority Queue kya hota hai
  • Kaise kaam karta hai (Heap concept)
  • Default behavior (Min-Heap)
  • Custom comparator ke saath use
  • Important methods aur examples

1️⃣ Priority Queue Kya Hota Hai?

Priority Queue ek queue hai jisme:

elements priority ke basis par process hote hain

FIFO (First In First Out) follow nahi karta.

2️⃣ Java me PriorityQueue

Class:

java.util.PriorityQueue

3️⃣ Internal Working

PriorityQueue internally use karta hai:

Heap (Binary Heap)

Default:

Min Heap

Matlab:

smallest element pehle niklega

4️⃣ Basic Example

import java.util.*;

class Test {

    public static void main(String[] args){

        PriorityQueue<Integer> pq = new PriorityQueue<>();

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

        System.out.println(pq);

        while(!pq.isEmpty()){
            System.out.println(pq.poll());
        }
    }
}

Output:

10
20
30

5️⃣ Important Methods

Method Use
add() insert element
offer() insert (safe)
peek() top element
poll() remove top
remove() delete

6️⃣ Min Heap vs Max Heap

Default:

Min Heap → smallest first

Max Heap banane ke liye:

PriorityQueue<Integer> pq = new PriorityQueue<>(Collections.reverseOrder());

7️⃣ Max Heap Example

PriorityQueue<Integer> pq = new PriorityQueue<>(Collections.reverseOrder());

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

while(!pq.isEmpty()){
    System.out.println(pq.poll());
}

Output:

30
20
10

8️⃣ Custom Comparator

PriorityQueue<Integer> pq = new PriorityQueue<>((a, b) -> b - a);

9️⃣ Custom Object Example

class Student {
    int marks;

    Student(int marks){
        this.marks = marks;
    }
}

Use:

PriorityQueue<Student> pq = new PriorityQueue<>(
    (s1, s2) -> s2.marks - s1.marks
);

pq.add(new Student(80));
pq.add(new Student(90));
pq.add(new Student(70));

while(!pq.isEmpty()){
    System.out.println(pq.poll().marks);
}

🔟 Priority Queue Properties

✔ elements sorted nahi dikhte
✔ head element highest priority hota hai
✔ duplicate allowed

1️⃣1️⃣ Use Cases

Dijkstra Algorithm
CPU Scheduling
Task Scheduling
Top K elements problems

1️⃣2️⃣ Difference from Queue

Feature Queue PriorityQueue
Order FIFO Priority based
Structure Linear Heap

1️⃣3️⃣ Important Points

✔ PriorityQueue thread-safe nahi hota
✔ null values allow nahi
✔ internal structure heap hota hai

🎯 Interview Questions

  1. PriorityQueue ka internal structure kya hai?
  2. Min heap aur max heap me difference?
  3. PriorityQueue me sorting kaise hoti hai?
  4. Custom comparator ka use kaise karte hain?

🧾 Lesson Summary

Is lesson me humne seekha:

✔ Priority Queue concept
✔ Heap working (Min/Max)
✔ Important methods
✔ Custom comparator
✔ Real-life usage

PriorityQueue Java me priority-based data processing ke liye use hota hai aur algorithms me bahut powerful hota hai.