Trying to understand Single Responsiblity Principle [closed]

Question

I'm having a difficult time understanding the Single Responsibility Principle.

What should I look for to evaluate the various sources of information on the matter?
What should I look for in examples explaining the principle?

Answer 1

SRP is a fairly straight-forward principle.

the single responsibility principle states that every object should have a single responsibility, and that responsibility should be entirely encapsulated by the class. All its services should be narrowly aligned with that responsibility.

-- http://en.wikipedia.org/wiki/Single_responsibility_principle

A class should have one, and only one, reason to change.

-- http://www.butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

Often, I find the second quote more applicable. I try to envision what my class does. What logic does it contain, or what external (to the class) services might it depend on.

I try to think about what might change, and how might this cause my class to change. Are there multiple things that could change and affect my class? That is a code smell (but not always reason enough to split a class).

Also, while I'm thinking along these lines, I look for cases where several classes will need to change if one other thing changes (logic, and external service, etc.). This too is a code smell.

Often, though, I have small groups of tightly coupled classes that coordinate or interact to perform a single function or service. If the changes occur across this set of tightly coupled classes, I find that ok. But if a change in, say, an external service requires changes in multiple classes in different areas of my application, that is a stinkier code smell.

Answer 2

Pluralsight has a course Principles of Object Oriented Design that covers SRP as the first topic in about 12 minutes. I believe you get a couple of hours of video for free, after that you need a subscription.