When a head of state dies, the president of the United States typically doesn’t have time to attend the funeral personally. Instead, he dispatches a delegate. Often, this delegate is the vice president, but sometimes the VP is unavailable, and the president must send someone else, such as the secretary of state or even the first lady. He doesn’t want to “hardwire” his delegated authority to a single person; he might delegate this responsibility to anyone who is able to execute the correct international protocol.
The president defines in advance what responsibility will be delegated (attend the funeral), what parameters will be passed (condolences, kind words), and what value he hopes to get back (good will). He then assigns a particular person to that delegated responsibility at “runtime” as the course of his presidency progresses.
In programming, you are often faced with situations where you need to execute a particular action, but you don’t know in advance which method, or even which object, you’ll want to call upon to execute it. The classic example of this is the method called to handle a button press, a menu selection, or some other “event.”
An event, in event-driven programming (like Windows!), is when something happens—often as a result of user action, but at times as a result of a change in system state or a result of a message begin received from outside the system (e.g., via the Internet).
You must imagine that the person who creates ...