How To Do Selection Sort Of ArrayList By Customer Last Name

I have an arrayList with these values:

Mike Smith with a customer id of 100 has an account number of 1000 and a balance of $5,000.00
Hank Jones with a customer id of 101 has an account number of 1001 and a balance of $45,000.00
Sam Overstreet with a customer id of 102 has an account number of 1002 and a balance of $45,000.00
Hank Jones with a customer id of 101 has an account number of 1003 and a balance of $48,000.00
and so on .....

I am trying to do a selection sort by the account holders last name. I understand how to do if the Arraylist holds integers, but my arraylist holds multiple fields. I am not allowed to use collections as this is a homework assignment.

here is the Account Class

public class Account implements Comparable<Account> {
private int acctNum;
private double balance;
private Customer cust; // note we are putting a Customer object in the Account clas
private static int nextAcct = 1000;// used to keep track of the next available account number

[Code] ....