Why would I ever use a Chain of Responsibility over a Decorator?

Question

I\'m just reading up on the Chain of Responsibility pattern and I\'m having trouble imagining a scenario when I would prefer its use over that of decorator.

What do

Answer 1

Decorator

1. Decorator pattern allows behaviour to be added to an individual object dynamically.

2. It provides a flexible alternative to sub classing for extending functionality. Even though it uses inheritance, it inherit from Lowest Common Denominator ( LCD ) interface.

UML diagram for Decorator

Consequences:

1. With decoration it is also possible to remove the added functionalities dynamically.
2. Decoration adds functionality to objects at runtime which would make debugging system functionality harder.

Useful links:

When to Use the Decorator Pattern?

Decorator_pattern from wikipedia

decorator from sourcemaking

Chain of responsibility:

Chain-of-responsibility pattern is a design pattern consisting of a source of command objects and a series of processing objects. Each processing object contains logic that defines the types of command objects that it can handle; the rest are passed to the next processing object in the chain

UML Diagram

This pattern is more effective when:

1. More than one object can handle a command
2. The handler is not known in advance
3. The handler should be determined automatically
4. It’s wished that the request is addressed to a group of objects without explicitly specifying its receiver
5. The group of objects that may handle the command must be specified in a dynamic way

Useful links:

Chain-of-responsibility_pattern from wikipedia

chain-of-responsibility-pattern from oodesign

chain_of_responsibility from sourcemaking

Real world example : In a company, a designated role have particular limits to process purchase request. If person with a designated role does not have enough power to approve purchase bill, he will forward the command/request to his successor, who have more power. This chain will continue until the command is processed.