Java in a Nutshell, 5th Edition

Naming and Capitalization Conventions

The following widely adopted naming conventions apply to packages, reference types, methods, fields, and constants in Java. Because these conventions are almost universally followed and because they affect the public API of the classes you define, they should be followed carefully:

Packages

Ensure that your publicly visible package names are unique by prefixing them with the inverted name of your Internet domain (e.g., com.davidflanagan.utils). All package names should be lowercase. Packages of code used internally by applications distributed in self-contained JAR files are not publicly visible and need not follow this convention. It is common in this case to use the application name as the package name or as a package prefix.

Reference types

A type name should begin with a capital letter and be written in mixed case (e.g., String). If a class name consists of more than one word, each word should begin with a capital letter (e.g., StringBuffer). If a type name, or one of the words of a type name, is an acronym, the acronym can be written in all capital letters (e.g., URL, HTMLParser).

Since classes and enumerated types are designed to represent objects, you should choose class names that are nouns (e.g., Thread, Teapot, FormatConverter).

When an interface is used to provide additional information about the classes that implement it, it is common to choose an interface name that is an adjective (e.g., Runnable, Cloneable, Serializable). ...