CSC/ECE 517 Fall 2011/ch4 4h lp

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.

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:

1. controls concurrent access to a shared resource.
2. access to the resource will be requested from multiple, disparate parts of the system.
3. there can be only one object.

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.

References

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