The assignment specified ensure a minimum of three pages (distinct) - customer, product and sales.
Home Products must be such to allow the introduction of a specific product, deleting an existing product, or the price of a product update example. The same applies to the Customer Support page. Home sales have existing products (introduced by Product page) to sell to customers (customers introduced through the corresponding page).
A suggestion is the MVC pattern.
To retain the memory of these entities can be achieved with HashMap classes.