Use cases

By using the Chain of Responsibility pattern, we give a chance to a number of different objects to satisfy a specific request. This is useful when we don't know which object should satisfy a request in advance. An example is a purchase system. In purchase systems, there are many approval authorities. One approval authority might be able to approve orders up to a certain value, let's say $100. If the order is more than $100, the order is sent to the next approval authority in the chain that can approve orders up to $200, and so forth.

Another case where Chain of Responsibility is useful is when we know that more than one object might need to process a single request. This is what happens in an event-based programming. A single event such as a left mouse click can be caught by more than one listener.

It is important to note that the Chain of Responsibility pattern is not very useful if all the requests can be taken care of by a single processing element, unless we really don't know...