How many classes should a programmer put in one fi

Question

In your object-oriented language, what guidelines do you follow for grouping classes into a single file? Do you always give each class a seperate file? Do you put tightly coupled classes together? Have you ever specified a couple of implementations of an interface in one file? Do you do it based on how many lines of code the implementation might be or how "cluttered" it might look to the user of the class? Or would the user prefer to have everything on one place?

Answer 1

I put classes into the same file if they belong together, either for techinical or aesthetic reasons. For example, in an application that provides a plugin interface, the classes Plugin (base class for plugins) and PluginManager I would usually put together in the same file. However, if the file grows too big for my taste, I would split them into separate file.

I note that I write code mostly in Python at the moment, and this influences my design. Python is very flexible in how I get to divide stuff into modules, and has good tools for managing the name spaces of things. For example, I usually put all the code for an application in a Python module (a directory with __init__.py) and have the module import specific names from sub-modules. The API is then something like applib.PluginManager rather than applib.pluginstuff.PluginManager.

This makes it easy to move things around, which also allows me to not be so fussy when I am creating the design: I can always fix things later.

Answer 2

In your object-oriented language, what guidelines do you follow for grouping classes into a single file?

It depends. In team work I try to follow team standards; in solo work I tend more towards whatever-I-please.

In solo work, then ...

Do you always give each class a seperate file? Do you put tightly coupled classes together? Have you ever specified a couple of implementations of an interface in one file?

No. Sometimes. Yes.

Do you do it based on how many lines of code the implementation might be or how "cluttered" it might look to the user of the class? Or would the user prefer to have everything on one place?

It's mostly based on:

• How easy is it to navigate? A huge long source file, with many classes, is more difficult.
• How easy is it to edit? When editing multiple, short, related classes, it may be easier if they're all in one source file with a splitter than if they're in several source files, given that I run my text editor maximized showing one source file at a time.

Answer 3

I prefer 1 to 1 for classes unless the inner class will be entirely private. Even then I usually break it out for ease of finding it and tracking changes in SVN.

Answer 4

I think best practices in all OO languages I have ever used is to have one class in one file. I believe some languages may require this but I am not sure of that fact. But I would say that one class per file, and the name of the file matching the name of the class (as well as the directory structure matching the package structure for the most part) is best-practice.

Answer 5

I try to keep one class per file (like most of the above), unless they are small classes. If there are a lot of them, I may split them into subjects otherwise. But usually I just keep them all in one file with code-folding in editors. For my private hacks, it just isn't worth the (minimal) effort to me.