什么是package-info.java

在java项目中创建package以后，可以在package下放一个package-info.java文件。

这个文件有什么作用？如何生成？

三个作用：

1. 为标注在包上Annotation提供便利；

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1. 声明友好类和包常量；

比如一个包中有很多的内部访问的类或常量，就可以统一的放到package-info类中，这样就方便，而且集中管理，减少friendly类到处游走的情况，看例子：

//这里是包类，声明一个包使用的公共类，强调的是包访问权限
class PkgClass{
    public void test(){
    }
}
//包常量，只运行包内访问，适用于分“包”开发
class PkgConst{
    static final String PACAKGE_CONST="ABC";
}

1. 提供包的整体注释说明。

Package Documentation
Prior to Java 5, package level documentation (the documentation shown in Javadocs for a package) was placed in package.html. Today, the description and other related documentation for a package can be written up in the package-info.java file and it gets used in the production of the Javadocs. As a demonstration, the example package-info.java…

/**
 * Domain classes used to produce the JSON and XML output for the RESTful services.
 * <p>
 * These classes contain the JAXB annotations.
 *
 * @since 1.0
 * @author jwhite
 * @version 1.1
 */
package com.intertech.cms.domain;

… results in the following Javadocs.

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package-info.java’s purpose
The package-info.java is a Java file that can be added to any Java source package. Its purpose is to provide a home for package level documentation and package level annotations. Simply create the package-info.java file and add the package declaration that it relates to in the file. In fact, the only thing the package-info.java file must contain is the package declaration.

1. 如何创建：

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参考

What’s package-info.java for?