java problem

1.Orders are processed on according to the date and time they were placed. A warehouse processes orders from a list by selecting the order that was placed the furthest in the past. Due to the distributed nature of this system, an order, A that was placed before another order, B, might be received at the warehouse after order B. What class should the warehouse use to hold the list of incoming orders?

2.Registered customers of an online merchant can save their shopping cart and when they log back in, their shopping cart is retrieved. The system is being designed so that the users login id (which is unique) is used to retrieve their shopping cart. It is desired that the retrieval of shopping carts be as fast as possible. What class should be used to hold the shopping carts?

3.We want to keep an alphabetical list of unique search terms a person types into a search engine. What class should we use to hold the terms.

4.A system processes very large amounts of text messages. Sending the texts is effectively instantaneous. However saving the text to the senders file is done as the server has time. So, after a text is sent, the text is placed at the end of a list. Periodically, the server will take the text at the front of the list and save it. What class should be used to hold the texts?