If you want to practice data structure and algorithm programs, you can go through data structure and algorithm interview questions.

In this post , we will see how to implement `Queue`

using Array in java.

`Queue`

is abstract data type which demonstrates **First in first out (FIFO)** behavior. We will implement same behavior using Array.

Although java provides implementation for all abstract data types such as `Stack`

, Queue and LinkedList but it is always good idea to understand basic data structures and implement them yourself.

Please note that `Array`

implementation of `Queue`

is not dynamic in nature.

There are two most important operations of Queue:

`enQueue:`

It is operation when we insert element into the queue.

`deQueue:`

It is operation when we remove element from the queue.

## Java Program to implement Queue using Array:

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package org.arpit.java2blog; public class QueueUsingArrayMain { private int capacity; int queueArr[]; int front; int rear; int currentSize = 0; public QueueUsingArrayMain(int sizeOfQueue) { this.capacity = sizeOfQueue; front = 0; rear = -1; queueArr = new int[this.capacity]; } /** * this method is used to add element in the queue * * @param data */ public void enqueue(int data) { if (isFull()) { System.out.println("Queue is full!! Can not add more elements"); } else { rear++; if (rear == capacity - 1) { rear = 0; } queueArr[rear] = data; currentSize++; System.out.println(data + " added to the queue"); } } /** * This method removes an element from the front of the queue */ public void dequeue() { if (isEmpty()) { System.out.println("Queue is empty!! Can not dequeue element"); } else { front++; if (front == capacity - 1) { System.out.println(queueArr[front - 1] + " removed from the queue"); front = 0; } else { System.out.println(queueArr[front - 1] + " removed from the queue"); } currentSize--; } } /** * This method is use to check if element is full or not * * @return boolean */ public boolean isFull() { if (currentSize == capacity) { return true; } return false; } /** * This method is use to check if element is empty or not * * @return */ public boolean isEmpty() { if (currentSize == 0) { return true; } return false; } public static void main(String a[]) { QueueUsingArrayMain queue = new QueueUsingArrayMain(5); queue.enqueue(6); queue.dequeue(); queue.enqueue(3); queue.enqueue(99); queue.enqueue(56); queue.dequeue(); queue.enqueue(43); queue.dequeue(); queue.enqueue(89); queue.enqueue(77); queue.dequeue(); queue.enqueue(32); queue.enqueue(232); } } |

When you run above program, you will get below output:

6 removed from the queue

3 added to the queue

99 added to the queue

56 added to the queue

3 removed from the queue

43 added to the queue

99 removed from the queue

89 added to the queue

77 added to the queue

56 removed from the queue

32 added to the queue

232 added to the queue

That’s all about Queue implementation in java.