When I run the code, it works, BUT, when I shut down the app all data get erased, it is not in memory. Can you help my to see a problem? I would like to save data for next run, because it's like a contact so users already know who they added.

File 1: PhoneBook.java

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

import java.util.Scanner;

public class PhoneBook {

static Scanner scnr = new Scanner(System.in);

// Declare a variable "contactInformation" and initializes it to an empty ArrayList

static List contactInformation = new ArrayList<>();

public static void main(String[] args) {

System.out.println("Hello! Welcome to Phone Book.");

//Display the Phone Book menu

String choice;

do {

System.out.println(); //Skip a line

System.out.println("Choose an option: ");

System.out.println("1. Add contact");

System.out.println("2. Delete contact");

System.out.println("3. Search contacts");

System.out.println("4. List contacts");

System.out.println("5. Fix contact.");

System.out.println("6. Exit");

System.out.print("Enter your choice: ");

choice = scnr.nextLine();

//a switch statement based on the user's inpu

switch (choice) {

case "1":

addContact(); //calls addContact method

break;

case "2":

deleteContactByName(); //calls deleteContact method

break;

case "3":

searchContact(); // calls searchContact method

break;

case "4":

listContact(); //calls listContact method

break;

case "5":

fixContact(); //calls fixContact method

break;

case "6":

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

break;

default:

System.out.println("Invalid choice. Try again."); //no choice exist

break;

}

} while (!choice.equals("6"));

}

// Add contact's information into the PhoneBook

public static void addContact() {

System.out.print("Enter contact's first name: "); //Prompt the user to enter contact's first name.

String firstName = scnr.nextLine();

System.out.print("Enter contact's last name: "); //Prompt the user to enter contact's last name.

String lastName = scnr.nextLine();

String email; //Declare email

while (true) {

System.out.print("Enter email (must contain @): "); //Prompt the user to enter email.

email = scnr.nextLine();

if (email.contains("@")) { //checks if the user enter email contains @

break;

}

else {

System.out.println("Invalid email address. Please enter an email address that contains '@'.");

}

}

String phoneNumber;

while (true) {

//Prompt the user to enter email.

System.out.print("Enter phone number (must follow format: xxx-xxx-xxxx): ");

phoneNumber = scnr.nextLine();

if (phoneNumber.matches("\\d{3}-\\d{3}-\\d{4}")) { // check if the phone number matches the format

break;

}

else {

System.out.println("Invalid phone number format. Please enter a phone number in the format of xxx-xxx-xxxx.");

}

}

ContactInformation newContact = new ContactInformation(firstName, lastName, email, phoneNumber);

contactInformation.add(newContact);

System.out.println(firstName + " " + lastName + "'s information has been added."); //Output the contact's first and last name that the user has been added.

}

// Delete contact's information from ContactInformation

public static void deleteContactByName() {

if (contactInformation.isEmpty()) {

System.out.println("No contacts to delete.");

return;

}

System.out.print("Enter the first name of the contact to delete: ");

String firstName = scnr.nextLine();

System.out.print("Enter the last name of the contact to delete: ");

String lastName = scnr.nextLine();

Iterator iter = contactInformation.iterator();

boolean foundContact = false;

while (iter.hasNext()) {

ContactInformation contact = iter.next();

if (contact.getFirstName().equalsIgnoreCase(firstName) &&

contact.getLastName().equalsIgnoreCase(lastName)) {

//Display contact's information

System.out.println("Name: " + contact.getFirstName() + " " + contact.getLastName() +

", Phone Number: " + contact.getPhoneNumber() +

", Email: " + contact.getEmail());

System.out.print("Do you want to delete this contact?(Yes/No): ");

String answer = scnr.nextLine();

if(answer.equalsIgnoreCase("Yes") || answer.equalsIgnoreCase("y")){

//Delete the contact

iter.remove();

System.out.println(contact.getFirstName() + " " + contact.getLastName() + " has been removed from the PhoneBook.");

}

else if(answer.equalsIgnoreCase("No") || answer.equalsIgnoreCase("n")){

System.out.println("Contact not deleted.");

}

else{

System.out.println("Invalid input. Contact not deleted.");

}

foundContact = true;

}

}

if (!foundContact) {

System.out.println("No contact found with the name " + firstName + " " + lastName);

}

}

// Search an entry

public static void searchContact() {

System.out.print("Enter search term: ");

String searchTerm = scnr.nextLine();

List matchingContacts = new ArrayList();

for (ContactInformation contact : contactInformation) {

if (contact.getFirstName().toLowerCase().contains(searchTerm.toLowerCase()) ||

contact.getLastName().toLowerCase().contains(searchTerm.toLowerCase()) ||

contact.getEmail().toLowerCase().contains(searchTerm.toLowerCase()) ||

contact.getPhoneNumber().toLowerCase().contains(searchTerm.toLowerCase())) {

matchingContacts.add(contact);

}

}

if (matchingContacts.size() == 0) {

System.out.println("No matching contacts found");

}

else {

System.out.println("Matching contacts: ");

for (ContactInformation contact : matchingContacts) {

System.out.println(contact);

}

}

}

// List contacts informations currently in PhoneBook.

public static void listContact() {

if (contactInformation.isEmpty()) {

System.out.println("Phone book is empty.");

}

else {

for (ContactInformation contact : contactInformation) {

System.out.println(contact);

}

}

}

public static void fixContact() {

System.out.print("Enter contact's first name: ");

String firstName = scnr.nextLine();

System.out.print("Enter contact's last name: ");

String lastName = scnr.nextLine();

Iterator iter = contactInformation.iterator();

while (iter.hasNext()) {

ContactInformation contact = iter.next();

if (contact.getFirstName().equals(firstName) && contact.getLastName().equals(lastName)) {

System.out.println("Enter field to fix:");

System.out.println("1. First name");

System.out.println("2. Last name");

System.out.println("3. Phone number");

System.out.println("4. Email");

System.out.print("Enter your choice: ");

String choice = scnr.nextLine();

switch (choice) {

case "1":

System.out.print("Enter new first name: ");

String newFirstName = scnr.nextLine();

contact.firstName = newFirstName;

System.out.println("First name updated.");

break;

case "2":

System.out.print("Enter new last name: ");

String newLastName = scnr.nextLine();

contact.lastName = newLastName;

System.out.println("Last name updated.");

break;

case "3":

String newPhoneNumber;

while (true) {

System.out.print("Enter new phone number (must follow format: xxx-xxx-xxxx): ");

newPhoneNumber = scnr.nextLine();

if (newPhoneNumber.matches("\\d{3}-\\d{3}-\\d{4}")) { // check if the phone number matches the format

break;

}

else {

System.out.println("Invalid phone number format. Please enter a phone number in the format of xxx-xxx-xxxx.");

}

}

contact.phoneNumber = newPhoneNumber;

System.out.println("Phone number updated.");

break;

case "4":

String newEmail; //Declare newEmail

while (true) {

System.out.print("Enter new email (must contain @): "); //Prompt the user to enter new email.

newEmail = scnr.nextLine();

if (newEmail.contains("@")) { //checks if the user enter email contains @

break;

}

else {

System.out.println("Invalid email address. Please enter an email address that contains '@'.");

}

}

contact.email = newEmail;

System.out.println("Email updated.");

break;

default:

System.out.println("Invalid choice. Try again.");

break;

}

return;

}

}

System.out.println("Contact not found.");

}

}

File 2: ContactInformation.java

import java.io.FileOutputStream;

import java.io.ObjectOutputStream;

import java.io.FileInputStream;

import java.io.ObjectInputStream;

public class ContactInformation {

public String firstName;

public String lastName;

public String email;

public String phoneNumber;

public ContactInformation(String firstName, String lastName, String email, String phoneNumber) {

this.firstName = firstName;

this.lastName = lastName;

this.email = email;

this.phoneNumber = phoneNumber;

}

//getter methods

public String getFirstName() {

return firstName;

}

public String getLastName() {

return lastName;

}

public String getEmail() {

return email;

}

public String getPhoneNumber() {

return phoneNumber;

}

@Override

public String toString() {

return "Name: " + firstName + " " + lastName + ", Phone number: " + phoneNumber + ", Email: " + email;

}

public static void saveData() {

try{

FileWriter fileWriter = new FileWriter("phonebook.txt");

PrintWriter printWriter = new PrintWriter(fileWriter);

for (ContactInformation contact : contactInformation) {

printWriter.println(contact.getFirstName() + "," + contact.getLastName() + "," +

contact.getEmail() + "," + contact.getPhoneNumber());

}

printWriter.close();

fileWriter.close();

System.out.println("Data saved successfully.");

}

catch (IOException e){

System.out.println("An error occurred while saving the data.");

e.printStackTrace();

}

}

public static void LoadData () {

try {

File file = new File("phonebook.txt");

Scanner scanner = new Scanner(file);

while (scanner.hasNextLine()) {

String line = scanner.nextLine();

String[] fields = line.split(",");

String firstName = fields[0];

String lastName = fields[1];

String email = fields[2];

String phoneNumber = fields[3];

ContactInformation contact = new ContactInformation(firstName, lastName, email, phoneNumber);

contactInformation.add(contact);

}

scanner.close();

System.out.println("Data loaded successfully.");

}

catch (FileNotFoundException e) {

System.out.println("The file was not found.");

}

}

}