Remember, One Class Per File

4 October, 2006. 268 words.

Another in a series of random programming tips by Thomas Krehbiel, mostly to help me remember them in the future.

Here’s something I’ve recently learned on the endless journey to software development perfection: Don’t put more than one class/definition in a single source file.

I know, I know, many of you are saying, “duh.” Everybody has bad habits they have to overcome in life. :)

When I first started working with Java, the one-class-per-file rule annoyed me a lot. I hated having to make a whole source file just for a two-line class. It seems really wasteful. Then when I started working with C#, I loved being able to put related classes together into one source file. I was back in the comfort of my old C programming days. I could put a collection class and the element class in the same file! And just for good measure, I could add an enum and a delegate declaration. Life was good.

Time passed. One day, I went back to work on some old code, and I realized much to my horror that you can’t freakin’ find anything when you’ve got more than one class in a single source file! The reason for the one-class-per-file rule became abundantly clear: It makes code maintenance a lot easier. You can just peek over at the Solution Explorer and find the file you need. (I suppose I could use the Class Explorer, but I never do.)

So now I’m “refactoring” some old code files and splitting them into one class per file, like they should have been in the first place. Lesson learned.

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