Not able to execute Login method. Feel something is wrong with the object creation for populating the array: Any help is very much appreciated

Question

Trying to create a bank management app. Not able to execute Login method after creating a new user. Feel something is wrong with the object creation for populating the Perons and Account arrays. Please help.

/Account class to hold account details/

public class Account extends Persons {

    int accountNum;
    int pin;
    float checkingBal;
    float savingBal;

    float withDrawAmount;
    float depositAmmount;
    float transferAmount;

    public  Account(){ }
    public Account(int accountNum, float checkingBal, float savingBal, int pin ){
        this.accountNum = accountNum;
        this.checkingBal = checkingBal;
        this.savingBal = savingBal;
        this.pin = pin;
    }

    public void setAccountNum(int accountNum){
        this.accountNum = accountNum;
    }

    public void setPin(int pin){
        this.pin = pin;
    }

    public int getAccountNum(){
        return accountNum;
    }

    public int getPin(){
        return pin;
    }


    public void withDraw(float withDrawAmount){

        this.savingBal = this.savingBal - withDrawAmount;
    }

    public void deposit(float depositAmmount){

        this.checkingBal = this.checkingBal + depositAmmount;
    }

    public void transfer(float transferAmount, String fromAccount, String toAccount){

        if(fromAccount == "Checking" && toAccount == "Savings"){

            this.checkingBal = this.checkingBal - transferAmount;
            this.savingBal = this.savingBal + transferAmount;
        }else if(fromAccount == "Savings" && toAccount == "Checking"){

            this.savingBal = this.savingBal - transferAmount;
            this.checkingBal = this.checkingBal + transferAmount;
        }

        System.out.print("Your New Checking Balance Is: "+this.checkingBal);
        System.out.print("Your New Savings Balance Is: "+this.savingBal);
    }

    public float checkBalance(int accountNum){
        float totalBalance = 0;
        if(this.accountNum == accountNum){
            totalBalance = this.checkingBal + this.savingBal;
        }
        return totalBalance;

    }
}

/*******************************************************************************************************/

/Persons class to hold all the people having account./

import java.util.Date;

public class Persons {

    String fname;
    String lname;
    int age;
    String dob;
    String address;
    float yearlyIncome;
    int accountNum;


    public Persons(){}
        public Persons(String fname, String lname, int age, String dob, String address, float yearlyIncome, int accountNum){
            this.fname = fname;
            this.lname = lname;
            this.age = age;
            this.dob = dob;
            this.address = address;
            this.yearlyIncome = yearlyIncome;
            this.accountNum = accountNum;
    }

    public void setFname(String fname) {
        this.fname = fname;
    }

    public void setLname(String lname) {
        this.lname = lname;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setDob(String dob) {
        this.dob = dob;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public void setYearlyIncome(float yearlyIncome) {
        this.yearlyIncome = yearlyIncome;
    }

    public void setAccountNum(int accountNum){
        this.accountNum = accountNum;
    }

    public String getFname() {
        return fname;
    }

    public String getLname() {
        return lname;
    }

    public int getAge() {
        return age;
    }

    public String getDob() {
        return dob;
    }

    public String getAddress() {
        return address;
    }

    public float getYearlyIncome() {
        return yearlyIncome;
    }

    public int getAccountNum(){
        return accountNum;
    }

}

/*****************************************************************************************************/

/Java Main Class/

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Random;
import java.util.Scanner;
import java.util.Date;

public class Main {

    public static void main(String[] args) {

        Scanner scanf = new Scanner(System.in);
        Persons people[] = new Persons[3];
        Account personAccount[] = new Account[3];


        float withdrawAmount;
        float depositAmount;
        float transferAmount;
        int mainChoice;
        int choice;
        int counter = 0;
        int userId = 0;
        int loopBreak = 0;
        int loginSuccess = -1;

        while(loopBreak != -1){
            System.out.println("================================================================================================");
            System.out.println("Welcome To The California Bank :)");
            System.out.println("1. Login..");
            System.out.println("2. Create A New Customer.");
            System.out.println("3. Done With Transactions.");


            mainChoice = scanf.nextInt();

            switch (mainChoice) {
                case 1:
                    System.out.println("Please Enter Your Account Number:");
                    int accountNum = scanf.nextInt();
                    System.out.println("Please Enter Your Pin:");
                    int pin = scanf.nextInt();

                    for (int i = 0; i <= counter; i++) {
                        if (personAccount[i].getAccountNum() == accountNum && personAccount[i].getPin() == pin) {
                            System.out.println(personAccount[i].getAccountNum());
                            System.out.println(personAccount[i].getPin());
                            System.out.println("Customer Logged In and Validated.");
                            userId = i;
                            loginSuccess = 0;
                        } else {
                            System.out.println("Sorry You Are Not A Current Customer!");
                            loginSuccess = -1;
                        }
                    }
                    if(loginSuccess == 0){
                        System.out.println("======================================================================================");
                        System.out.println("What Else Would You Like To Do Today?");
                        System.out.println("1. Deposit.");
                        System.out.println("2. Withdraw.");
                        System.out.println("3. Transfer Money.");
                        System.out.println("4. Check Balance.");
                        choice = scanf.nextInt();

                        switch (choice) {
                            case 1:
                                System.out.println("How Much Money Would You Like To Deposit?");
                                depositAmount = scanf.nextFloat();
                                personAccount[userId].deposit(depositAmount);
                                break;

                            case 2:
                                System.out.println("How Much Money Would You Like To Withdraw Today?");
                                withdrawAmount = scanf.nextFloat();
                                personAccount[userId].withDraw(withdrawAmount);
                                break;

                            case 3:
                                System.out.println("How Much Money Would You Like To Withdraw Today?");
                                transferAmount = scanf.nextFloat();
                                System.out.println("1. Press 1 To Transfer From Checking to Savings.");
                                System.out.println("2. Press 2 To Transfer From Savings To Checking.");
                                int transferChoice;
                                transferChoice = scanf.nextInt();
                                if (transferChoice == 1) {
                                    personAccount[userId].transfer(transferAmount, "Checking", "Savings");
                                } else {
                                    personAccount[userId].transfer(transferAmount, "Savings", "Checking");
                                }
                            case 4:
                                System.out.println("Here Is Your Total Account Balance");
                                personAccount[userId].checkBalance(people[counter].accountNum);
                                break;
                        }

                    }
                    break;
                case 2:
                    people[counter] = new Persons();
                    personAccount[counter] = new Account();
                    System.out.println("Please Enter Your First Name For The Account Creation:");
                    scanf.next();
                    String fName = scanf.nextLine();
                    System.out.println("Please Enter Your Last Name For The Account Creation:");
                    scanf.next();
                    String lName = scanf.nextLine();
                    people[counter].setFname(fName);
                    people[counter].setLname(lName);
                    System.out.println("Please Enter Your Age:");
                    int age = scanf.nextInt();
                    people[counter].setAge(age);
                    System.out.println("Please Enter Your Date Of Birth:");
                    String dob = scanf.next();
                    people[counter].setDob(dob);
                    System.out.println("Please Enter Your Address:");
                    scanf.next();
                    String address = scanf.nextLine();
                    people[counter].setAddress(address);
                    System.out.println("Please Enter Your Yearly Income:");
                    float annualIncome = scanf.nextFloat();
                    people[counter].setYearlyIncome(annualIncome);
                    System.out.println("Generating Your Account Number.....");
                    Random rand = new Random();
                    accountNum = rand.nextInt(100000);
                    people[counter].setAccountNum(accountNum);
                    personAccount[counter].setAccountNum(accountNum);
                    System.out.println("Your New Account Number Is: "+accountNum);
                    System.out.println("Please Enter A 4 Digit Pin");
                    pin = scanf.nextInt();
                    personAccount[counter].setPin(pin);

                    System.out.println("New Customer Created:");
                    counter++;
                    break;

                case 3:
                    System.out.println("Thanks For Using The California Banking System. Goodbye!");
                    loopBreak = -1;
                    break;

              }

            }

        }

    }

Below is the error I am Getting after creating a user:

1. Login..
2. Create A New Customer.
3. Done With Transactions. 1 Please Enter Your Account Number: 90806 Please Enter Your Pin: 3333 90806 3333 Customer Logged In and Validated. Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Account.getAccountNum()" because "personAccount[i]" is null at Main.main(Main.java:48)

Answer 1

There are so many things about your code, but first its explanation about your bug which is NullPointerException.

This exception is thrown when you for example try to call some methods on null elements. In your case you declared array as 3 elements and add only one Account (newly created). Then you iterate on array which have null elements (2nd and 3rd are null). You should get rid of this for loop or initialize array as 1 element sized = new Account[1] and then each time copy your new accounts to new array with bigger size. But it would be terrible solution. Another way (much better

Arrays are not size dynamic so you should use one of Collections https://www.javatpoint.com/collections-in-java for example List (ArrayList would be enough). I will show you how to improve your code, hope you will learn something from it.

Ok so here is the code:

Person (not persons, shouldn't be), don't use float for money, use BigDecimal, mark your fields as private or protected (read about encapsulation), descript your fields better, not like dob - write dateOfBirth, I use LocalDate here, dont use old Time api, better look at new Java Time Api, also you can count age of user by: currentDate - dateOfBirth

import java.math.BigDecimal;
import java.time.LocalDate;
import java.time.LocalDateTime;

public class Person {

    private String firstName;
    private String lastName;
    private int age;
    private LocalDate dateOfBirth;
    private String address;
    private BigDecimal yearlyIncome;
    private int accountNumber;

    public Person() { }

    public Person(String firstName, String lastName, int age, LocalDate dateOfBirth, String address, BigDecimal yearlyIncome, int accountNumber) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
        this.dateOfBirth = dateOfBirth;
        this.address = address;
        this.yearlyIncome = yearlyIncome;
        this.accountNumber = accountNumber;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public LocalDate getDateOfBirth() {
        return dateOfBirth;
    }

    public void setDateOfBirth(LocalDate dateOfBirth) {
        this.dateOfBirth = dateOfBirth;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public BigDecimal getYearlyIncome() {
        return yearlyIncome;
    }

    public void setYearlyIncome(BigDecimal yearlyIncome) {
        this.yearlyIncome = yearlyIncome;
    }

    public int getAccountNumber() {
        return accountNumber;
    }

    public void setAccountNumber(int accountNumber) {
        this.accountNumber = accountNumber;
    }
}

Ok, next Account You should read about super() keyword to call methods or constructors from parent class, I used it here just to show you how to do it, you give it to parent and set account class fields

import java.math.BigDecimal;

public class Account extends Person {

    private int accountNumber;
    private int pin;
    private BigDecimal checkingBalance = BigDecimal.ZERO;
    private BigDecimal savingBalance = BigDecimal.ZERO;

    public Account() { }

    public Account(int accountNumber, int pin, BigDecimal checkingBalance, BigDecimal savingBalance){
        this.accountNumber = accountNumber;
        this.checkingBalance = checkingBalance;
        this.savingBalance = savingBalance;
        this.pin = pin;
    }

    public int getAccountNumber() {
        return accountNumber;
    }

    public void setAccountNumber(int accountNumber) {
        this.accountNumber = accountNumber;
    }

    public int getPin() {
        return pin;
    }

    public void setPin(int pin) {
        this.pin = pin;
    }

    public void withDraw(BigDecimal withDrawAmount){
        this.savingBalance = this.savingBalance.subtract(withDrawAmount);
    }

    public void deposit(BigDecimal depositAmmount){
        this.checkingBalance = this.checkingBalance.subtract(depositAmmount);
    }

    public void transfer(BigDecimal transferAmount, String fromAccount, String toAccount){

        if(fromAccount.equals("Checking") && toAccount.equals("Savings")){
            this.checkingBalance = this.checkingBalance.subtract(transferAmount);
            this.savingBalance = this.savingBalance.add(transferAmount);
        }else if(fromAccount.equals("Savings") && toAccount.equals("Checking")){
            this.savingBalance = this.savingBalance.subtract(transferAmount);
            this.checkingBalance = this.checkingBalance.add(transferAmount);
        }

        System.out.print("Your New Checking Balance Is: " + this.checkingBalance);
        System.out.print("Your New Savings Balance Is: " + this.savingBalance);
    }

    public BigDecimal checkBalance(){
        return this.checkingBalance.add(this.savingBalance);
    }
}

Main

I improve a little Main class, you can see that I use List personsAccount, Collections are dynamic you can add as many elements as you want, means that you use collection of type account, you can do it like List too but read about inheritance and generics first. I add 5th option to back to main menu, also use do while option, 1 list is enough, you don't need persons and accounts arrays.

import java.math.BigDecimal;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.Scanner;

public class Main {

    private static final Scanner scanner = new Scanner(System.in);
    //if you use java 8 or above you can just do it like = new ArrayList<>();
    //static is here just because of example, you should reconsider it
    private static final List<Account> personsAccounts = new ArrayList<Account>();

    public static void main(String[] args) {
        BigDecimal withdrawAmount;
        BigDecimal depositAmount;
        BigDecimal transferAmount;

        int mainChoice;
        int choice;
        boolean session = true;
        Account currentLoggedAccount = new Account();
        int loginSuccess = -1;

        while (session) {
            System.out.println("================================================================================================");
            System.out.println("Welcome To The California Bank :)");
            System.out.println("1. Login..");
            System.out.println("2. Create A New Customer.");
            System.out.println("3. Done With Transactions.");

            mainChoice = scanner.nextInt();

            switch (mainChoice) {
                case 1:
                    System.out.println("Please Enter Your Account Number:");
                    int accountNumber = scanner.nextInt();

                    System.out.println("Please Enter Your Pin:");
                    int pin = scanner.nextInt();

                    for (int i = 0; i < personsAccounts.size(); i++) {
                        if (personsAccounts.get(i).getAccountNumber() == accountNumber && personsAccounts.get(i).getPin() == pin) {
                            System.out.println(personsAccounts.get(i).getAccountNumber());
                            System.out.println(personsAccounts.get(i).getPin());
                            System.out.println("Customer Logged In and Validated.");
                            currentLoggedAccount = personsAccounts.get(i);
                            loginSuccess = 0;
                        } else {
                            System.out.println("Sorry You Are Not A Current Customer!");
                            loginSuccess = -1;
                        }
                    }
                    if (loginSuccess == 0) {
                        do {
                            System.out.println("======================================================================================");
                            System.out.println("What Else Would You Like To Do Today?");
                            System.out.println("1. Deposit.");
                            System.out.println("2. Withdraw.");
                            System.out.println("3. Transfer Money.");
                            System.out.println("4. Check Balance.");
                            System.out.println("5. Back to main menu");
                            choice = scanner.nextInt();
                            switch (choice) {
                                case 1:
                                    System.out.println("How Much Money Would You Like To Deposit?");
                                    depositAmount = scanner.nextBigDecimal();
                                    currentLoggedAccount.deposit(depositAmount);
                                    break;
                                // is case 2 and 3 is the same?
                                case 2:
                                    System.out.println("How Much Money Would You Like To Withdraw Today?");
                                    withdrawAmount = scanner.nextBigDecimal();
                                    currentLoggedAccount.withDraw(withdrawAmount);
                                    break;
                                case 3:
                                    System.out.println("How Much Money Would You Like To Withdraw Today?");
                                    transferAmount = scanner.nextBigDecimal();
                                    System.out.println("1. Press 1 To Transfer From Checking to Savings.");
                                    System.out.println("2. Press 2 To Transfer From Savings To Checking.");
                                    int transferChoice;
                                    transferChoice = scanner.nextInt();
                                    if (transferChoice == 1) {
                                        currentLoggedAccount.transfer(transferAmount, "Checking", "Savings");
                                    } else {
                                        currentLoggedAccount.transfer(transferAmount, "Savings", "Checking");
                                    }
                                    break;
                                case 4:
                                    System.out.println("Here Is Your Total Account Balance");
                                    currentLoggedAccount.checkBalance();
                                    break;
                                default:
                                    System.out.println("There is no option :(");
                                    break;
                            }
                        }
                        while (choice != 5);
                    }
                    break;
                case 2:
                    Account accountToAdd = new Account();

                    System.out.println("Please Enter Your First Name For The Account Creation:");
                    scanner.next();
                    String firstName = scanner.nextLine();
                    accountToAdd.setFirstName(firstName);

                    System.out.println("Please Enter Your Last Name For The Account Creation:");
                    scanner.next();
                    String lastName = scanner.nextLine();
                    accountToAdd.setLastName(lastName);

                    System.out.println("Please Enter Your Age:");
                    int age = scanner.nextInt();
                    accountToAdd.setAge(age);

                    System.out.println("Please Enter Your Date Of Birth:");
                    String date = scanner.next();
                    DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd.MM.yyyy");
                    accountToAdd.setDateOfBirth(LocalDate.parse(date, dtf));

                    System.out.println("Please Enter Your Address:");
                    scanner.next();
                    String address = scanner.nextLine();
                    accountToAdd.setAddress(address);

                    System.out.println("Please Enter Your Yearly Income:");
                    BigDecimal annualIncome = scanner.nextBigDecimal();
                    accountToAdd.setYearlyIncome(annualIncome);

                    System.out.println("Generating Your Account Number.....");
                    Random rand = new Random();
                    //that is some kind of weir because what if somebody have this number yet? :D
                    int newAccountNumber = rand.nextInt(100000);

                    accountToAdd.setAccountNumber(newAccountNumber);
                    System.out.println("Your New Account Number Is: " + newAccountNumber);
                    System.out.println("Please Enter A 4 Digit Pin");
                    pin = scanner.nextInt();
                    accountToAdd.setPin(pin);

                    //adding new account to list
                    personsAccounts.add(accountToAdd);
                    System.out.println("New Customer Created:");
                    break;
                case 3:
                    System.out.println("Thanks For Using The California Banking System. Goodbye!");
                    session = false;
                    break;
                default:
                    System.out.println("There is no option :(");
                    break;
            }
        }
    }
}

This code isn't perfect but it's working and its clearer, it can be improved by you as you wish. Hope you will learn something, read about java.Collections, java.Time, java Generics, you can also exchange normal for to for each loop like for(Account account : personsAccounts) {}. Cheers!