Chain of Responsibility

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Chain of Responsibility (Behavioral Pattern)

• The Chain of Responsibility pattern uses a chain of objects to handle a request, which is typically an event. Objects in the chain forward the request along the chain until one of the objects handles the event. Processing stops after an event is handled.

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Purpose

• Is to avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.

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UML Diagram

The role of every class:

• Handler - defines an interface for handling requests
• ConcreteHandler:
  • handles the requests it is responsible for
  • If it can handle the request it does so, otherwise it sends the request to its successor
• Client - sends commands to the first object in the chain that may handle the command

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Applicability

Here are a few situations when using the Chain of Responsibility is more effective:

• More than one object can handle a request

• The handler is not known in advance

• The handler should be determined automatically

• It’s wished that the request is addressed to a group of objects without explicitly specifying its receiver

• The group of objects that may handle the request must be specified in a dynamic way

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External Links

• External Links

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--Djeyarat 15:49, 2 April 2007 (EDT)