How to manage ATM Bank accounts w/ Java

How to manage ATM Bank accounts w/ Java

This is a two part question. Pt. 1: I am trying to make an ATM program in
Java just for fun and practice in the language, but I do not know how to
create and store 'users' if you will. I have this class made.
public class User {
// Creating userCode var as data type integer.
private int userCode;
// Creating PIN var as data type integer.
private int PIN;
// Creating a savings account balance.
private double savingsAccount;
// Creating a checking account balance.
private double checkingAccount;
I need to know how to create new accounts with a chosen userCode and PIN,
'save' them, and then when a user enters their code, find their account
and load in their current balances and PIN.
Pt. 2: How can I create a database to store the user's balances, etc.
permanetly on my computer in a pList, or some other data storage file.
Thanks!!