How to implement queue in java by using array, a code by vasu

Queue is important concept in computer science.

It is a liner data structure, that do supports a FIFO behavior (First In First Out). It is very useful data structure. 

This very good code of queue is implemented by 

Vasu Gupta / IT / Maharaja Agrasen Institute of Technology (Delhi)

In this code the queue is implemented using array. I will also update queue implementation using linked list very soon.

# save this class inside Queue.java file #

import java.util.Scanner;

// Create a class Queue consisting of main method in it

public class Queue {

// Declare some static Variables

static int front = -1 , rear = -1 , max = 5 ;

static int[] queue = new int[max];

static int data ;

public static void main(String[] args) {

// Create Scanner class object

Scanner sc = new Scanner(System.in);

// Get user input data again and again

do {

System.out.print("Enter the data : ");

data = sc.nextInt();

add(data); // Push the data into the queue

System.out.print("Do you want to add more (y/n");

}

                 while(sc.next().equals("y"));

// Show the queue data : 

System.out.print("Queue : ");

showData();

// Remove first element out of  queue (FIFO Mechanism)

System.out.print("\nRemoving one element out : ");

delete();

showData();

}

// Create static method add() so that it can be accessed in the static main method

public static void add(int data) {

// Check if queue is full

if(rear == max-1) {

System.out.println("Queue is Full");

} else if(front == -1 && rear == -1) {

front++ ; // Increment front by one

rear++ ; // Increment rear by one

queue[rear] = data ; // Add data to the queue at last of the queue

} else {

rear++ ; 

queue[rear] = data ;

}

}

public static void delete() {

// Check if queue is empty

if(front == -1 && rear == -1) {

System.out.println("Empty Queue");

} else {

queue[front] = 0 ; // Remove element from front

front++ ; // Increment front by one

}

}

// Function to show the data of the queue

public static void showData() {

for (int i = front; i < rear; i++) {

System.out.print(queue[i] + "-->");

}

System.out.println(queue[rear]);

}

}

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