BankAccountSimulation.java

import java.util.Scanner;

/**
 * BankAccountSimulation class contains the main method to run a console-based bank account simulation.
 * It provides an interactive menu for users to create accounts, perform banking transactions,
 * and view balance/transaction histories.
 */
public class BankAccountSimulation {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Account activeAccount = null;

        System.out.println("=================================================");
        System.out.println("      WELCOME TO BANK ACCOUNT SIMULATION         ");
        System.out.println("=================================================");

        boolean running = true;
        while (running) {
            System.out.println("\n---------------- MAIN MENU ----------------");
            System.out.println("1. Create New Bank Account");
            System.out.println("2. Deposit Money");
            System.out.println("3. Withdraw Money");
            System.out.println("4. Check Balance");
            System.out.println("5. View Transaction History");
            System.out.println("6. Apply Interest (Savings Account Only)");
            System.out.println("7. Exit");
            System.out.print("Choose an option (1-7): ");

            int choice = readIntegerInput(scanner);

            switch (choice) {
                case 1:
                    activeAccount = createAccountMenu(scanner);
                    break;

                case 2:
                    if (checkAccountExists(activeAccount)) {
                        System.out.print("Enter deposit amount: Rs. ");
                        double amount = readDoubleInput(scanner);
                        activeAccount.deposit(amount);
                    }
                    break;

                case 3:
                    if (checkAccountExists(activeAccount)) {
                        System.out.print("Enter withdrawal amount: Rs. ");
                        double amount = readDoubleInput(scanner);
                        activeAccount.withdraw(amount);
                    }
                    break;

                case 4:
                    if (checkAccountExists(activeAccount)) {
                        activeAccount.displayBalance();
                    }
                    break;

                case 5:
                    if (checkAccountExists(activeAccount)) {
                        activeAccount.showTransactionHistory();
                    }
                    break;

                case 6:
                    if (checkAccountExists(activeAccount)) {
                        // Check if the active account is a SavingsAccount (Polymorphism)
                        if (activeAccount instanceof SavingsAccount) {
                            SavingsAccount savings = (SavingsAccount) activeAccount;
                            savings.applyInterest();
                        } else {
                            System.out.println("Error: Interest can only be applied to a Savings Account.");
                            System.out.println("Current active account is a Standard Account.");
                        }
                    }
                    break;

                case 7:
                    System.out.println("\nThank you for using Bank Account Simulation! Goodbye.");
                    running = false;
                    break;

                default:
                    System.out.println("Invalid option. Please select a number between 1 and 7.");
            }
        }
        scanner.close();
    }

    /**
     * Menu to guide the user through creating a new account (Standard or Savings).
     */
    private static Account createAccountMenu(Scanner scanner) {
        System.out.println("\n--- Create Account ---");
        System.out.println("Select Account Type:");
        System.out.println("1. Standard Account");
        System.out.println("2. Savings Account (Enforces Rs. 500 Min Balance + Interest)");
        System.out.print("Enter choice (1-2): ");
        int type = readIntegerInput(scanner);

        if (type != 1 && type != 2) {
            System.out.println("Invalid choice. Aborting account creation.");
            return null;
        }

        System.out.print("Enter Account Number: ");
        String accNum = scanner.nextLine().trim();
        while (accNum.isEmpty()) {
            System.out.print("Account number cannot be empty. Enter Account Number: ");
            accNum = scanner.nextLine().trim();
        }

        System.out.print("Enter Account Holder Name: ");
        String accHolder = scanner.nextLine().trim();
        while (accHolder.isEmpty()) {
            System.out.print("Account holder name cannot be empty. Enter Account Holder Name: ");
            accHolder = scanner.nextLine().trim();
        }

        System.out.print("Enter Initial Deposit: Rs. ");
        double initialDeposit = readDoubleInput(scanner);
        while (initialDeposit < 0) {
            System.out.print("Initial deposit cannot be negative. Enter Initial Deposit: Rs. ");
            initialDeposit = readDoubleInput(scanner);
        }

        Account newAccount;
        if (type == 1) {
            newAccount = new Account(accNum, accHolder, initialDeposit);
            System.out.println("\nStandard Account successfully created!");
        } else {
            // For SavingsAccount, we can also customize interest rate or use default
            System.out.print("Enter annual interest rate (e.g. 3.5 for 3.5%, or press Enter to use default 3.5%): ");
            String rateInput = scanner.nextLine().trim();
            if (rateInput.isEmpty()) {
                newAccount = new SavingsAccount(accNum, accHolder, initialDeposit);
            } else {
                try {
                    double rate = Double.parseDouble(rateInput) / 100.0;
                    if (rate < 0) {
                        System.out.println("Invalid interest rate. Using default 3.5%.");
                        newAccount = new SavingsAccount(accNum, accHolder, initialDeposit);
                    } else {
                        newAccount = new SavingsAccount(accNum, accHolder, initialDeposit, rate);
                    }
                } catch (NumberFormatException e) {
                    System.out.println("Invalid number format. Using default 3.5%.");
                    newAccount = new SavingsAccount(accNum, accHolder, initialDeposit);
                }
            }
            System.out.println("\nSavings Account successfully created!");
        }

        newAccount.displayBalance();
        return newAccount;
    }

    /**
     * Check if an active account exists. Displays an error if not.
     */
    private static boolean checkAccountExists(Account account) {
        if (account == null) {
            System.out.println("Error: No active account found. Please create an account first (Option 1).");
            return false;
        }
        return true;
    }

    /**
     * Safely reads an integer input, handling invalid text inputs to prevent program crash.
     */
    private static int readIntegerInput(Scanner scanner) {
        while (true) {
            try {
                String input = scanner.nextLine().trim();
                return Integer.parseInt(input);
            } catch (NumberFormatException e) {
                System.out.print("Invalid input. Please enter a valid integer option: ");
            }
        }
    }

    /**
     * Safely reads a double input, handling invalid text inputs to prevent program crash.
     */
    private static double readDoubleInput(Scanner scanner) {
        while (true) {
            try {
                String input = scanner.nextLine().trim();
                return Double.parseDouble(input);
            } catch (NumberFormatException e) {
                System.out.print("Invalid input. Please enter a valid decimal number: Rs. ");
            }
        }
    }
}