Applying Design Patterns - Part I and II

This article is expected to: [1] Introduce patterns to you in a simple, human readable way [2] Train you how to really 'Apply' patterns (you can learn patterns easily, but to apply them to solve a problem, you need real design skills) [3] Provide you a fair idea regarding the contexts for applying the following patterns - Builder, Observer, Strategy and Decorator (well, they are few popular design patterns) [4] Demonstrate you how to apply the Observer pattern, to solve a design problem