Basic Internet banking application

I programmed in Java before, but I feel that I lack the "true way" of programming (OOP concepts, design, algorithm), so I started to learn all of these but I need your opinions and suggestions so I can improve my skills and to be sure that I got all the concepts right. I know that there are multiple ways of doing some things, but I am trying to learn the most efficient and the best practices ways.

Application description:

• A user is prompted to insert his login credentials (account number and account password).

• If an account number is found in the database then the password is verified (in this case I have a HashMap with the key holding the account number and the value holding the account to whom the account number belongs).

-
After a successful login, the user has two choices:

• Check account balance

• Deposit money

InternetBankingApp.java class:

```
package main;

import java.util.HashMap;

import accounts.Account;
import operations.AccountOperations;
import operations.OperationFactory;
import utils.InputScanner;

public class InternetBankingApp {

private static boolean successLogin;

private static InputScanner input;
private static HashMap accounts;
private static Account userAccount;

public static void main(String[] args) {

accounts = new HashMap();
successLogin = false;

Account account1 = new Account(1, "password1", 1000.00);
Account account2 = new Account(2, "password2", 2000.00);
Account account3 = new Account(3, "password3", 3000.00);

accounts.put(account1.getAccountNo(), account1);
accounts.put(account2.getAccountNo(), account2);
accounts.put(account3.getAccountNo(), account3);

login();

if(successLogin) {
performOperation();
}

}

private static void login() {
int loginTries = 0;

input = InputScanner.getInstance();

System.out.println("Enter Account no.: ");
String userIn

Dessign Issue

In your daily codding life just remember one thing:
The Best Code is Not Code At All

You have an additional wrapper for Scanner. You will need to refactor, maintain this code in the future.

InputScanner are used in 2 places in the code, we can replace it with builtin Scanner:

Example for AccountDeposit

Scanner sc = new Scanner(System.in);
double userInputBalance = sc.NextDouble(); // this line is more shortly than initial

The same you can do in main method.
Possible Error Issue

I want to check if user input is correct, because user can write any number and this number can be negative or equal to zero.

double userInputBalance = 
            Double.parseDouble(InputScanner.getInstance().readInput());

boolean isBalanceCorrect = checkInputBalance(userInputBalance);

if (isBalanceCorrect) {
  balance += userInputBalance;  
  account.setBalance(balance);

  System.out.println("New account balance: " + account.getBalance());
} // else you can call this function again or to do something

Additional function for checking user input.

private boolean checkInputBalance(double inputBalance) {
  if (inputBalance < 0) {
    System.out.println("You can't insert negative values on your deposit");
    return false;
  } else if (inputBalance == 0) {
    System.out.println("You current balance will not change");
    return false;        
  }
}

StackExchange Code Review Q#130118, answer score: 2