Project scene:
Today, the training room has a new teacher and talks about the backstage teacher. There was a problem reinstalling jdk, and the environment variables have not been properly configured. The teacher said that the issue of matching java jdk environment variables has always been a metaphysics, and I was thinking about metaphysics belching, isn't it just missing a symbol.
Problem Description:
C:\Users\Administrator>javac
'javac' 不是内部或外部命令，也不是可运行的程序
或批处理文件。
C:\Users\Administrator>
Cause Analysis:
In the configuration environment variable path pay more when a semicolon ";"
C: \ Program Files \ nodejs; the back end of the semicolon to be deleted, and then add. 
In fact, you can find the Path variable directly in the system variables. This Path is your own, so you don't need to add Path yourself! ! ! Just add it at the end and it's done.
The semicolon ";" is really a headache,
solution:
Just remove the nodesjs\ ";" behind him . Just add it.
;%JAVA_HOME%\bin;%JAVA_HOME%\jre\bin
It doesn't matter if the last semicolon is added or not. After adding, cmd enters javac and prompts as follows and 
it is successful.