Private jre vs Public jre

今天说一下java环境构建中，jre相关的小知识点。

private jre：一般是C:\Program Files\jdk1.8.0\jre，必须安装，它为jdk的运行提供必需的环境。

public jre：一般是C:\Program Files\Java\jre1.8.0，可以选择安装。

如果，平时更新java版本，那么将会在public jre的目录下，添加新版本的jre。有人认为，public jre是多余的，会浪费磁盘空间，对于SSD来说，110M的空间还是很宝贵的，private jre足已。在某些Eclipse集成java版本中，里面就仅使用了private jre，可以应对运行的需求了。

可是，如果有一些java版本的匹配的需求的话，public jre应该就会体现它的作用了。

官方文档（https://docs.oracle.com/javase/8/docs/technotes/guides/install/windows_jdk_install.html#CHDJCCEG）如下：

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Installing the JDK also installs a private JRE and optionally a public copy. The private JRE is required to run the tools included with the JDK. It has no registry settings and is contained entirely in a jre directory (typically at C:\Program Files\jdk1.8.0\jre) whose location is known only to the JDK. On the other hand, the public JRE can be used by other Java applications, is contained outside the JDK (typically at C:\Program Files\Java\jre1.8.0), is registered with the Windows registry (at HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft), can be removed using Add/Remove Programs, might be registered with browsers, and might have the java.exe file copied to the Windows system directory (which would make it the default system Java platform).

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