Question

I have a really long problem. I am creating a bank account and setting the balance to 0. If the user chooses to withdraw or deposit money to the account, the balance never changes. I choose to show the balance and it still says 0. This is probably a no brainer but I am spent right now. Here is my long code(The switch statement is in my main class and the methods are in an object class):

public class MyProgram2{
public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    Scanner input = new Scanner (System.in);
    String menu, outputString, poo;
    int option = 1;
    int id = 0;
    double balance = 0, amount = 0;
    Account acc = new Account();


    menu ="\n\t1  Create Account and ID" + 
            "\n\t2  Check balance" +
            "\n\t3  Withdraw" +
            "\n\t4  Deposit" + 
            "\n\t5  Get account ID" +
            "\n\t6  Display Account Info" +

            "\n\t0  Quit\n\n\n";

    System.out.println(menu);
    System.out.println("\tEnter your selection:  ");
    option = scan.nextInt();

    while (option != 0) {

            switch (option) {

            case 1: //Create an account and set ID
                        System.out.print("Enter Your Account ID to create account:\t");
                        id = input.nextInt();
                        System.out.println("Account created!");
                        break;

            case 2:     //check balance
                        acc.checkBalance(balance);
                        break;

            case 3:     //withdraw money
                        acc.withdraw(balance, amount);
                        break;

            case 4: //deposit money
                        acc.deposit(balance, amount);
                        break;

            case 5:     //get account id
                        acc.getID(id);
                        break;

            case 7:     //display account info
                        System.out.print("option 7");
                        break;

            default: outputString = "\nInvalid Selection\n";
                        System.out.println(outputString);
                        break;

        }
    System.out.println(menu);
    System.out.print("\tEnter your selection:   ");
    option = scan.nextInt();    
    }

And these are the methods I am calling:

public class Account{
Scanner input = new Scanner (System.in);

public Account(){
}

public void getID(int id){
    System.out.println("Your account ID is:\t" + id);
}

public void checkBalance(double balance){
    System.out.println("Your balance is:\t$" + balance);
}

public double withdraw(double amount, double balance){
    System.out.println("How much do you want to withdraw?:\t$");
    amount = input.nextDouble();
    balance -= amount;
    return balance;
}

public double deposit(double amount, double balance){
    System.out.println("How much do you want to deposit?:\t");
    amount = input.nextDouble();
    balance += amount;
    return balance;
}

public void getAccountInfo(int id, double balance){

}
}

Answer 1

The variable

double balance

cannot be passed as a reference. It does a copy so when you try to manipulate it, it won’t affect the original that you pass as an argument. You need to update the value using the return value that you have in the function.

In order to make it work, you should do:

case 4: //deposit money

// note here that you need to update the balance variable using the return value that
// you put in the function
balance = acc.deposit(balance, amount);
break;

Note: Your design separating the balance from the Account class is not ideal per @Psyrus’s answer. You should keep the balance as part of the Account class. The reason being that balance is part of the account and if your program grows to handle multiple accounts (just for the sake of examples), separating the variable balance from the account would create maintenance headache (imagine that with two instances of Account, you will have balance1 and balance2 variables (or whatever you will call it) in MyProgram2, the main application). While I gave the cause of your problem in regards of variable passing, you should refactor your code to follow @Psyrus suggestion.