### Queue Data Structure - The Coding Shala

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## Queue Data Structure

In this post, we will see the basics of the queue. The queue is a Data Structure, also known as the First-in-first-out data structure(FIFO). In a queue, there are two main operations: Enqueue and Dequeue. The insert Operation is called enqueue and the new element is always added at the end of the queue. The delete operation is called dequeue and we only allowed to remove the first element.

## Queue Java Program

The following is a simple implementation of the queue:

import java.util.ArrayList; import java.util.List; //Queue implementation class MyQueue{ //to store data private List<Integer> data; private int q_start; //start point of queue //initial state MyQueue(){ data = new ArrayList<Integer>(); q_start = 0; } //Enqueue Operation //add element at the end of queue are return true if successful public boolean EnQueue(int element) { data.add(element); return true; } //DeQueue operation //remove element if there any //move start pointer public boolean DeQueue() { if(isEmpty()) return false; q_start++; return true; } //check is empty or not public boolean isEmpty() { if(data.size() <= q_start) return true; return false; } //return first element public int Front(){ if(isEmpty()) return -1; return data.get(q_start); } } public class Main{ public static void main(String[] args) { MyQueue queue = new MyQueue(); queue.EnQueue(4); queue.EnQueue(5); queue.EnQueue(6); if(queue.isEmpty() == false) { //check if not empty System.out.println("First Element is: "+queue.Front()); } queue.DeQueue(); if(queue.isEmpty() == false) { //check if not empty System.out.println("First Element is: "+queue.Front()); } queue.DeQueue(); System.out.println("First Element is: "+queue.Front()); queue.DeQueue(); //now queue is empty will return -1 System.out.println("First Element is: "+queue.Front()); if(queue.isEmpty() == false) { //check if not empty System.out.println("First Element is: "+queue.Front()); }else { System.out.println("Queue is Empty"); } } }

First Element is: 4 First Element is: 5 First Element is: 6 First Element is: -1 Queue is Empty

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