11- Map and flatMap (Coding Part)

Create a code using concepts of  map() and flatMap() in which data is taken from customer like (id , name , email and phone numbers) . In which every customer has one emailId but one or more than one phone numbers 

Customer

package com.java.map;

import java.util.List;

public class Customer {

   

     private int id;

        private String name;

        private String email;

        private List<String> phoneNumbers;

        public Customer() {

        }

        public Customer(int id, String name, String email, List<String> phoneNumbers) {

            this.id = id;

            this.name = name;

            this.email = email;

            this.phoneNumbers = phoneNumbers;

        }

        public int getId() {

            return id;

        }

        public void setId(int id) {

            this.id = id;

        }

        public String getName() {

            return name;

        }

        public void setName(String name) {

            this.name = name;

        }

        public String getEmail() {

            return email;

        }

        public void setEmail(String email) {

            this.email = email;

        }

        public List<String> getPhoneNumbers() {

            return phoneNumbers;

        }

        public void setPhoneNumbers(List<String> phoneNumbers) {

            this.phoneNumbers = phoneNumbers;

        }

}

EkartDataBase

package com.java.map;

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

import java.util.stream.Stream;

public class EkartDataBase {

   

     public static List<Customer> getAll() {

            return Stream.of(

                    new Customer(101, "john", "john@gmail.com", Arrays.asList("397937955", "21654725")),

                    new Customer(102, "smith", "smith@gmail.com", Arrays.asList("89563865", "2487238947")),

                    new Customer(103, "peter", "peter@gmail.com", Arrays.asList("38946328654", "3286487236")),

                    new Customer(104, "kely", "kely@gmail.com", Arrays.asList("389246829364", "948609467"))

            ).collect(Collectors.toList());

        }

}

MapVsFlatMap

package com.java.map;

import java.util.List;

import java.util.stream.Collectors;

public class MapVsFlatMap {

   

     public static void main(String[] args) {

            List<Customer> customers = EkartDataBase.getAll();

                       //customer -> customer.getEmail()  one to one mapping

            List<String> emails = customers.stream()

                    .map(customer -> customer.getEmail())

                    .collect(Collectors.toList());

            System.out.println(emails);

           

            System.out.println("-------------------------------------------");

                      //customer -> customer.getPhoneNumbers()  ->> one to many mapping

            List<List<String>> phoneNumbers = customers.

                    stream().map(customer -> customer.getPhoneNumbers())

                    .collect(Collectors.toList());

            System.out.println(phoneNumbers);

            System.out.println("-------------------------------------------");

           

                         //FlatMap Transformation of PhoneNumbers

                         //customer -> customer.getPhoneNumbers()  ->> one to many mapping

            List<String> phones = customers.stream()

                    .flatMap(customer -> customer.getPhoneNumbers().stream())

                    .collect(Collectors.toList());

            System.out.println(phones);

        }

}

CONSOLE

[john@gmail.com, smith@gmail.com, peter@gmail.com, kely@gmail.com]

-------------------------------------------

[[397937955, 21654725], [89563865, 2487238947], [38946328654, 3286487236], [389246829364, 948609467]]

-------------------------------------------

[397937955, 21654725, 89563865, 2487238947, 38946328654, 3286487236, 389246829364, 948609467]