说明：  一个安装在不同操作系统的Java虚拟机负责着Java程序与操作系统之间的工作，因此每个Java虚拟机的系统环境属性是不同的，我们可以通过访问Java虚拟机的系统属性来获知一些关于当前操作系统的一些基本信息，这些信息的价值有时是非常重要的
(a different operating system installed in the Java virtual machine for Java with the operating system and procedures between the work, so every Java Virtual Machine System environmental attributes are different. We can visit the Java Virtual Machine System attribute to learn that some of the current systems of some of the basic information , the value of this information is sometimes a very important)