The Single Responsibility Principle (SRP)

Simply put: A class should have one and only one task to perform. Or another way to put it: A class should have one and only one reason to exist. Object Mentor says it (and describes it) best at http://www.objectmentor.com/resources/articles/srp.pdf

The single responsibility principle is one of those things that sounds too theoretical. How can a class have just a single task to do? What if my system has 1000 tasks to be performed, do I have to create 1000 classes? Well, YES :-). And I am here to tell you that this principle works, in practice.

What did I gain by following this principle?

1. Improved the maintainability of my code: Since a class does only one thing, I can touch it w/o breaking any code that does other things. Simple :-)
2. Improved the extensibility of my code:

And the drawbacks?

1. The so called 'Class Explosion'. Your application may end up with too many classes to manage.
2. Yes, I can change code in classes without worrying too much about affecting other code, but first I have to find the code I need to change. And with myriad of classes it can get tricky to pinpoint what you want to change