A real-life example

When we go to the restaurant for dinner, we give the order to the waiter. The check (usually paper) they use to write the order on is an example of Command. After writing the order, the waiter places it in the check queue that is executed by the cook. Each check is independent and can be used to execute many and different commands, for example, one command for each item that will be cooked. The following figure, courtesy of www.sourcemaking.com [j.mp/cmdpattern], shows a sequence diagram of a sample order: