What's the best approach to naming classes?

Question

Coming up with good, precise names for classes is notoriously difficult. Done right, it makes code more self-documenting and provides a vocabulary for reasoning about code at a higher level of abstraction.

Classes which implement a particular design pattern might be given a name based on the well known pattern name (e.g. FooFactory, FooFacade), and classes which directly model domain concepts can take their names from the problem domain, but what about other classes? Is there anything like a programmer's thesaurus that I can turn to when I'm lacking inspiration, and want to avoid using generic class names (like FooHandler, FooProcessor, FooUtils, and FooManager)?

Answer 1

I'll cite some passages from Implementation Patterns by Kent Beck:

Simple Superclass Name

"[...] The names should be short and punchy. However, to make the names precise sometimes seems to require several words. A way out of this dilemma is picking a strong metaphor for the computation. With a metaphor in mind, even single words bring with them a rich web of associations, connections, and implications. For example, in the HotDraw drawing framework, my first name for an object in a drawing was DrawingObject. Ward Cunningham came along with the typography metaphor: a drawing is like a printed, laid-out page. Graphical items on a page are figures, so the class became Figure. In the context of the metaphor, Figure is simultaneously shorter, richer, and more precise than DrawingObject."

Qualified Subclass Name

"The names of subclasses have two jobs. They need to communicate what class they are like and how they are different. [...] Unlike the names at the roots of hierarchies, subclass names aren’t used nearly as often in conversation, so they can be expressive at the cost of being concise. [...]

Give subclasses that serve as the roots of hierarchies their own simple names. For example, HotDraw has a class Handle which presents figure- editing operations when a figure is selected. It is called, simply, Handle in spite of extending Figure. There is a whole family of handles and they most appropriately have names like StretchyHandle and TransparencyHandle. Because Handle is the root of its own hierarchy, it deserves a simple superclass name more than a qualified subclass name.

Another wrinkle in subclass naming is multiple-level hierarchies. [...] Rather than blindly prepend the modifiers to the immediate superclass, think about the name from the reader’s perspective. What class does he need to know this class is like? Use that superclass as the basis for the subclass name."

Interface

Two styles of naming interfaces depend on how you are thinking of the interfaces. Interfaces as classes without implementations should be named as if they were classes (Simple Superclass Name, Qualified Subclass Name). One problem with this style of naming is that the good names are used up before you get to naming classes. An interface called File needs an implementation class called something like ActualFile, ConcreteFile, or (yuck!) FileImpl (both a suffix and an abbreviation). In general, communicating whether one is dealing with a concrete or abstract object is important, whether the abstract object is implemented as an interface or a superclass is less important. Deferring the distinction between interfaces and superclasses is well >supported by this style of naming, leaving you free to change your mind later if that >becomes necessary.

Sometimes, naming concrete classes simply is more important to communication than hiding the use of interfaces. In this case, prefix interface names with “I”. If the interface is called IFile, the class can be simply called File.

For more detailed discussion, buy the book! It's worth it! :)