trying to understand some java concepts

Question

This is probably a silly questions but its something I am trying to understand. I have 2 classes: a Person class and an Account class. In the Account class I have a 3 methods to set an account balance, to withdraw from that balance, and to return that balance. If I created a new object for a new Person and a new Account how do I tie them together? By together I mean how do I know when I try and get the the account balance, that I am getting it for a specific person and not just anyones balance? (assuming I have multiple account and person objects).

• PM 77-1: What are the properties of your Account object?

Answer 1

You connect them together by placing the Account (Wouldn't be a mistake to make it a Array of Accounts) object into the Person object. and then access the appropriate account using the Person:

class Person
{
 String name;
 String id;
 ...
 List<Account> ownedAccounts = new ArrayList<Account>();
}

• Aubin: And if a Person owns several Accounts?
• Laabidi Raissi: I think, the reverse is more compliant. Account objects should refer to Person
• Aubin: And for married people with a joined account?
• user4815162342: @Aubin Married couples would simply share the same Account object in their respective ownedAccounts lists.

Answer 2

You can add field in Person class for instance:

ArrayList<Account> accounts;

or you can add some field in Account class (if only one person can be owner otherwise you will also need some list or set):

Person person;

Answer 3

The way that makes sense to me is to have an account object reference in the Person class.

class Person { Account account; }

and then you can add a checkAccount method to the person class.

void checkBalance(){ return account.getBalance(); }

Then wherever you have a Person object you can call

person.checkBalance();

To make sure that the account is that person's you should pass the Account object in the constructor of the Person object.

Person(Account account){ this.account = account }

Or you could have a setter method. If every person in the system must have an account then passing it in the constructor is a better idea.

• Aubin: And if a Person owns several Accounts?
• eytanfb: The question doesn't specify that. But if it did using a List<Account> and having an addAccount() method would make sense