Sort an ArrayList of objects?

Question

I need some help how to sort an ArrayList of objects. I have the superclass Account and two subclasses SavingsAccount and CreditAccount. Inside the Account class I have this met

Answer 1

java.util.Collections.sort(list) - use it when Account implements Comparable.

java.util.Collections.sort(list, new Comparator(){
     public int compare(Account a,  Account b){
          return a.getAccountNumber().compareTo(b.getAccountNumber()
     }
});