Loading

Queue Interface

 

  • Queue is the linear data structure that follows a first-in-first-out (FIFO) order. The implementation classes of Queue Interface are  Priority Queue and LinkedList.
  • Queue is a pre-defined Interface present in java.util package, Introduced from JDK1.5.

Important Methods of Queue

  • enQue() - This method will add an object into Queue at the rear end.
  • deQue() - This method will remove the object from the Queue from the front end.
  • isFull() - returns true if the Queue is full.
  • isEmpty() - returns true if Queue is empty.
  • display() - returns all the objects present in Queue.

Priority Queue

Key points:

  • Priority Queue is an Implementation class of Queue Interface.
  • Present in java.util pack and introduced from JDK1.5 
  • Only comparable type objects can be inserted in the Priority Queue.

Methods of Priority Queue 

Method

Description

boolean add(object);It is used to insert the element into this queue and return true upon success.
Object remove();It is used to remove the head object of this queue.
Object poll();It is used to remove the object object from the head, or return null if Queue is empty.
Object peak();It is used to retrieve or read the head object  of this Queue. Or return null if the retrieveQueue is empty.
Object element();It is used to retrieves, but doesn't remove, the head of this Queue.

Example:

package com.quipoin;

import java.util.PriorityQueue;

public class QueueDemo {
	public static void main(String[] args) {
		PriorityQueue<Integer> queue=new PriorityQueue<>();
		queue.add(10);
		queue.add(20);
		queue.add(30);
		queue.add(40);
		queue.add(50);

		System.out.println(queue);

		queue.poll();//retrieves and removes head element
		System.out.println(queue);
		System.out.println("--------------------");
		queue.clear();//This method will clear the elements from the Queue.
		System.out.println(queue);
	}
}

Output:

[10, 20, 30, 40, 50]
[20, 40, 30, 50]