CSC/ECE 517 Fall 2011/ch4 4h lp: Difference between revisions
Jump to navigation
Jump to search
| Line 10: | Line 10: | ||
===Singleton=== | ===Singleton=== | ||
[http://en.wikipedia.org/wiki/Singleton_pattern Singleton] is a design pattern which imposes a restriction on the class to instantiate exactly one object of that class. | [http://en.wikipedia.org/wiki/Singleton_pattern Singleton] is a design pattern which imposes a restriction on the class to instantiate exactly one object of that class. | ||
====When should we use Singleton ?==== <ref>[http://stackoverflow.com/questions/228164/on-design-patterns-when-to-use-the-singleton When should we use Singleton ?]</ref> | |||
For an object to be considered as a singleton object, they must satisfy three requirements: | |||
#controls concurrent access to a shared resource. | |||
#access to the resource will be requested from multiple, disparate parts of the system. | |||
#there can be only one object. | |||
====Uses==== | ====Uses==== | ||
====Advantages==== | |||
*Singletons are often preferred to global variables as they don't pollute the global [http://en.wikipedia.org/wiki/Namespace namespace] with unnecessary variables & also can be instantiated only when needed unlike global variables which always consume resources. | |||
====Drawbacks==== | ====Drawbacks==== | ||
*Introduces a global state into the application. | |||
*Can make unit testing classes in isolation difficult. | |||
===Adapter=== | ===Adapter=== | ||
Revision as of 02:42, 21 October 2011
Introduction
This wiki article discusses about some of the commonly used & easy to understand Desgin patterns[1] in the software industry. Specifically, we will be studying about the Singleton, Adapter, Command & Strategy patterns.
Design Pattern
Definition
Examples
Case Study
Singleton
Singleton is a design pattern which imposes a restriction on the class to instantiate exactly one object of that class. ====When should we use Singleton ?==== <ref>When should we use Singleton ?</ref> For an object to be considered as a singleton object, they must satisfy three requirements:
- controls concurrent access to a shared resource.
- access to the resource will be requested from multiple, disparate parts of the system.
- there can be only one object.
Uses
Advantages
- Singletons are often preferred to global variables as they don't pollute the global namespace with unnecessary variables & also can be instantiated only when needed unlike global variables which always consume resources.
Drawbacks
- Introduces a global state into the application.
- Can make unit testing classes in isolation difficult.
Adapter
Command
Strategy
Conclusion
References
<references/>