A class CustomerService is defined to resolve customer service requests in the order in which they are received.

The details of the members of the class are given below:
Class name: CustomerService
Data members/instance variables:
services[]: array to store customer service request
size: to store the maximum capacity of the array
first: to store the index of the first customer service request
last: to store the index of the last customer service request
Methods/Member functions:
CustomerService(int s): constructor to assign size = s, first = 0 and last = 0
void add(int reqst): to insert a request at index last, if space is available, otherwise display “Request cannot be accepted at the moment”
int del(): to remove and return the request at index first, if any, else return -9999.

(i) Specify the class CustomerService giving details of the functions void add(int) and int del(). Assume that the other functions have been defined.

import java.util.Scanner;
class CustomerService{
    int services[];
    int size;
    int first;
    int last;
    public CustomerService(int s){
        size = s;
        services = new int[size];
        first = 0;
        last = 0;
    }
    public void add(int reqst){
        if(last < size)
            services[last++] = reqst;
        else
            System.out.println("Request cannot be accepted at the moment.");
    }
    public int del(){
        if(first < last){
            int reqst = services[first];
            first++;
            return reqst;
        }
        return -9999;
    }
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        System.out.print("Array capacity: ");
        int n = in.nextInt();
        CustomerService obj = new CustomerService(n);
        while(true){
            System.out.println("1. Add request");
            System.out.println("2. Delete request");
            System.out.print("Enter your choice: ");
            int choice = in.nextInt();
            switch(choice){
                case 1:
                    System.out.print("Enter request: ");
                    int r = in.nextInt();
                    obj.add(r);
                    break;
                case 2:
                    int d = obj.del();
                    if(d == -9999)
                        System.out.println("Queue Empty");
                    else
                        System.out.println("Deleted request: " + d);
                    break;
                default:
                    System.out.println("Bye...");
                    return;
            }
        }
    }
}

(ii) Name the entity described above and state its principle.
The entity described above is the Queue Data Structure. It works on the FIFO (First In First Out) principle.