Queue

Java Queue interface orders the element in FIFO(First In First Out) manner. In FIFO, first element is removed first and last element is removed at last.

Operations

Function	What it does?	Complexity
boolean add(object)	It is used to insert the specified element into this queue and return true upon success.	O(log(n))
boolean offer(object)	It is used to insert the specified element into this queue.	O(log(n))
Object remove()	It is used to retrieves and removes the head of this queue.	O(log(n))
Object poll()	It is used to retrieves and removes the head of this queue, or returns null if this queue is empty.	O(1)
Object peek()	It is used to retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.	O(1)

Priority Queues

Java Priority Queue is implemented using Heap Data Structures

Implementions

// Java progrm to demonstrate working of priority queue in Java
import java.util.*;
 
class Example
{
    public static void main(String args[])
    {
       
        PriorityQueue<String> pQueue =
                          new PriorityQueue<String>();
 
        pQueue.add("Shivam");
        pQueue.add("Neel");
        pQueue.add("Devansh");

        System.out.println("Head value using peek function:"
                                           + pQueue.peek());
 
        System.out.println("The queue elements:");
        Iterator itr = pQueue.iterator();
        while (itr.hasNext())
            System.out.println(itr.next());
 
        pQueue.poll();
        System.out.println("After removing an element" +
                           "with poll function:");
        Iterator<String> itr2 = pQueue.iterator();
        while (itr2.hasNext())
            System.out.println(itr2.next());
 
        pQueue.remove("Neel");
        System.out.println("after removing Java with" +
                           " remove function:");
        Iterator<String> itr3 = pQueue.iterator();
        while (itr3.hasNext())
            System.out.println(itr3.next());
 
 
        }
}

Output:

Head value using peek function:Shivam
The queue elements:
Shivam
Neel
Devansh

After removing an elementwith poll function:
Neel
Devansh
after removing Neel with remove function:
Devansh