站内搜索: 请输入搜索关键词
当前页面: 在线文档首页 > Java Tutorial 5.0 英文版

Naming a Package - Java Tutorial 5.0 英文版

The JavaTM Tutorial
Previous Page Lesson Contents Next Page Start of Tutorial > Start of Trail > Start of Lesson Search
Feedback Form

Trail: Learning the Java Language
Lesson: Interfaces and Packages

Naming a Package

With programmers worldwide writing classes, interfaces, enums, and annotations using the Java programming language, it is likely that two programmers will use the same name for two different classes. 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. Why? Because they are in different packages, and the fully qualified name of each 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 is java.awt.Rectangle.

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


By Convention:  Companies use their reversed Internet domain name in their package names (for example, com.company.package). 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.company.region.package).

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 use an underscore. For example:

Domain name Package name
clipart-open.org org.clipart_open
free.fonts.int int_.fonts.free
poetry.7days.com com._7days.poetry


Previous Page Lesson Contents Next Page Start of Tutorial > Start of Trail > Start of Lesson Search
Feedback Form

Copyright 1995-2005 Sun Microsystems, Inc. All rights reserved.