CSC/ECE 517 Fall 2011/ch4 4h lp: Difference between revisions
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===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 ? | ====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: | For an object to be considered as a singleton object, they must satisfy three requirements: | ||
#controls concurrent access to a shared resource. | #controls concurrent access to a shared resource. | ||
Revision as of 02:43, 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/>