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Ilkka Seppälä 2020-08-29 11:29:30 +03:00
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@ -9,27 +9,32 @@ tags:
---
## Intent
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.
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.
## Explanation
Real world example
> The Orc King gives loud orders to his army. The closest one to react is the commander, then officer and then soldier. The commander, officer and soldier here form a chain of responsibility.
> The Orc King gives loud orders to his army. The closest one to react is the commander, then
> officer and then soldier. The commander, officer and soldier here form a chain of responsibility.
In plain words
> It helps building a chain of objects. Request enters from one end and keeps going from object to object till it finds the suitable handler.
> It helps to build a chain of objects. A request enters from one end and keeps going from an object
> to another until it finds a suitable handler.
Wikipedia says
> In object-oriented design, the 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.
> In object-oriented design, the 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.
**Programmatic Example**
Translating our example with orcs from above. First we have the request class
Translating our example with the orcs from above. First we have the `Request` class:
```java
public class Request {
@ -140,14 +145,16 @@ king.makeRequest(new Request(RequestType.COLLECT_TAX, "collect tax")); // Orc so
```
## Class diagram
![alt text](./etc/chain.urm.png "Chain of Responsibility class diagram")
## Applicability
Use Chain of Responsibility when
* more than one object may handle a request, and the handler isn't known a priori. The handler should be ascertained automatically
* you want to issue a request to one of several objects without specifying the receiver explicitly
* the set of objects that can handle a request should be specified dynamically
* More than one object may handle a request, and the handler isn't known a priori. The handler should be ascertained automatically.
* You want to issue a request to one of several objects without specifying the receiver explicitly.
* The set of objects that can handle a request should be specified dynamically.
## Real world examples