Java-Tutorials-8-Java-Naming a Java Package

September 15, 2016

 

Naming a Package

With programmers worldwide writing classes and interfaces using the Java programming language, it is likely that many programmers will use the same name for different types. In fact, the previous example does just that: It defines a Rectangle class when there is already a Rectangle class in the java.awt package. Still, the compiler allows both classes to have the same name if they are in different packages. The fully qualified name of each Rectangle class includes the package name. That is, the fully qualified name of the Rectangle class in the graphics package is graphics.Rectangle, and the fully qualified name of the Rectangle class in the java.awt package isjava.awt.Rectangle.

This works well unless two independent programmers use the same name for their packages. What prevents this problem? Convention.

Naming Conventions

Package names are written in all lower case to avoid conflict with the names of classes or interfaces.

Companies use their reversed Internet domain name to begin their package names—for example, com.example.mypackage for a package named mypackage created by a programmer at example.com.

Name collisions that occur within a single company need to be handled by convention within that company, perhaps by including the region or the project name after the company name (for example, com.example.region.mypackage).

Packages in the Java language itself begin with java. or javax.

In some cases, the internet domain name may not be a valid package name. This can occur if the domain name contains a hyphen or other special character, if the package name begins with a digit or other character that is illegal to use as the beginning of a Java name, or if the package name contains a reserved Java keyword, such as “int”. In this event, the suggested convention is to add an underscore. For example:

Legalizing Package Names
Domain Name Package Name Prefix
hyphenated-name.example.org org.example.hyphenated_name
example.int int_.example
123name.example.com com.example._123name

Naming Conventions

Naming conventions make programs more understandable by making them easier to read. They can also give information about the function of the identifier-for example, whether it’s a constant, package, or class-which can be helpful in understanding the code.


Identifier Type

Rules for Naming

Examples

Packages
The prefix of a unique package name is always written in all-lowercase ASCII letters and should be one of the top-level domain names, currently com, edu, gov, mil, net, org, or one of the English two-letter codes identifying countries as specified in ISO Standard 3166, 1981.

Subsequent components of the package name vary according to an organization’s own internal naming conventions. Such conventions might specify that certain directory name components be division, department, project, machine, or login names.

 com.sun.eng

com.apple.quicktime.v2

edu.cmu.cs.bovik.cheese

Classes
Class names should be nouns, in mixed case with the first letter of each internal word capitalized. Try to keep your class names simple and descriptive. Use whole words-avoid acronyms and abbreviations (unless the abbreviation is much more widely used than the long form, such as URL or HTML).
class Raster;
class ImageSprite;

Interfaces
Interface names should be capitalized like class names.
interface RasterDelegate;
interface Storing;

Methods
Methods should be verbs, in mixed case with the first letter lowercase, with the first letter of each internal word capitalized.
run();
runFast();
getBackground();

Variables
Except for variables, all instance, class, and class constants are in mixed case with a lowercase first letter. Internal words start with capital letters. Variable names should not start with underscore _ or dollar sign $ characters, even though both are allowed.

Variable names should be short yet meaningful. The choice of a variable name should be mnemonic- that is, designed to indicate to the casual observer the intent of its use. One-character variable names should be avoided except for temporary “throwaway” variables. Common names for temporary variables are i, j, k, m, and n for integers; c, d, and e for characters.


Constants
The names of variables declared class constants and of ANSI constants should be all uppercase with words separated by underscores (“_”). (ANSI constants should be avoided, for ease of debugging.)
static final int MIN_WIDTH = 4;

static final int MAX_WIDTH = 999;

static final int GET_THE_CPU = 1;
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