Hi... For example, if I have a ShoppingCart object which contains an ArrayList of lineItem objects. Each lineitem object contains the attribute productName, productPrice, productCode, and quantity. Here's the expected behavior. For example... initially it's sorted by productCode, productName, productPrice, and quantity. If the user clicks productName then it will be sorted by productName, productCode, productPrice, and quantity. If the user clicks productPrice then it will be sorted by productPrice, productName, productCode, and quantity. and so on... Initially I planned to use Comparator but this can only be used for sorting a single column. How do I implement such functionality? thank you very much your help will be very much appreciated.