The good news is, I am practcing:
package structure;a


/**
 * Represents a Bank Account , has a account that doesn’t change, a balance, that does change.
 *
 * @author Alex Stoneham
 * @version 1
 */
public class BankAccount
{

    /**
     * The Account Number
     */
    protected String account;

    /**
     * The Balance Associated with the account.
     */
    protected double balance;


    /**
     * Precondition account is a string  identifying the bank account
     * balance is thr starting balance
     * post: constructs a bank account with the desired balance
     */
    public BankAccount(String acc, double bal)
    {

        account = acc;
        balance = bal;
    }

    /**
     * pre: other is a valid BankAccount
     * post: returns true if this account is the same as the other
     */
    public boolean equeals(Object other)
    {
        BankAccount that = (BankAccount)other;
        // two accounts are the same if account numbers are the same.
        return this.account.equals(that.account);
    }

    /**
     * post: Returns the bank account number of this account
     */
    public String getAccount()
    {
       return account;
    }

    /**
     * post retuns the balance of this bank account
     */
    public double getBalance()
    {
        return balance;
    }


    /**
     * post: deposit money in the bank account
     */
    public void deposit(double amount)
    {
        balance = balance + amount;
    }

    /**
     * pre: there are sufficent funds in the account
     * post: withdraw money from the bank account
     */
    public void withdraw(double amount)
    {
        balance = balance - amount;
    }



    public static void main(String[] args)
    {
        // Question: is it better to invest $100 over 10 years at 5%
        //              or to ivest $100 over 20 years at 2.5% intrest

        BankAccount jd = new BankAccount("John Dough", 100.00);
        BankAccount js = new BankAccount("John Smith", 100.00);

        for (int years = 0; years < 10; years++)
        {
            jd.deposit(jd.getBalance() * 0.05);
        }

        for (int years = 0; years < 20; years++)
        {
            js.deposit(js.getBalance() * 0.025);
        }


        System.out.println("John D invests $100 over 10 years at 5%.");
        System.out.println("After 10 years " + jd.getAccount() +
                            " has $" + jd.getBalance());

        System.out.println("John S invests $100 over 20 years at 2.5%");
        System.out.println("After 20 years " + js.getAccount() +
                            " has $" + js.getBalance());


    }




}