Beginner needs help

[ddonn]

I am trying to create a new BankAccount object with an initial balance, the withdraw an amount from that object. I, then want to display the amount after the withdrawal using JOptionPane showMessageDialog method.
I have 2 files, the BankAccount class file(attached) which I compiled and another file which calls methods from the BankAccount file.
When I try to compile the second file I get an error saying "cannot find variable balance".
I have tried declaring a variable balance but then I get an error saying "variable balance might not have been initialised".
Can anyone point me in the right direction?? Any help would be much appriciated.
Thanks in advance.

import javax.swing.JOptionPane;
public class FixedStartingBankBalanceAccount
{
public static void main(String[] args)
{


//Constructor; calls constructor method from BankAccount class
BankAccount myFirstAccount = new BankAccount(5000);// Creates new BankAccount object with an initial balance

//***Methods***

//Calls withdraw method from BankAccount class
myFirstAccount.withdraw(200);//balance = balance - amount

//Calls getBalance method from BankAccount class
myFirstAccount.getBalance();//Retrieves balance from myFirstAccoun object

JOptionPane.showMessageDialog(null, "myFirstAccount contains:" + balance);
}
}

[JosAH]

Look at your last two lines of code (ignore empty lines and curly brackets for now): what is getBalance() doing? Is it returning the balance value of the account? Why aren't you storing (assigning) it somewhere? And, what is that (undeclared) variable 'balance' doing in your last line of code?

kind regards,

Jos

[ddonn]

OK I understand the problem there, but if i put something like, "double balance;" into my code I still get an error saying variable balance may not be initialised.
I suppose where I am getting confused is when I call a method from the BankAccount class e.g myFirstAccount.withdraw(200); it goes to that class and does something like this, balance = balance - amount;
Do I need to declare all variables e.g balance and amount and if so how do I do it because double balance;
double amount; doesnt work.
Kind regards.

[ddonn]

I think i need to declare instance fields, where the declaration requires an access specifier, type and name of variable e.g private double balance.

I just don't know where to do this.

Can anyone assist?

Thanks in advance

[gcalvin]

Just put your getBalance() call right in your showMessageDialog() call. You don't need a variable, let alone an instance variable.