Open Environment Variables dialog.

In the System variables below, new a varible named JAVA_HOME and the value is the path where JDK was installed.

Then edit Path variable, insert the text below into the foremost:

%Java_Home%\bin;%Java_Home%\jre\bin;

Finally, new a variable named CLASSPATH,the value is as follow:

.;%Java_Home%\bin;%Java_Home%\lib\dt.jar;%Java_Home%\lib\tools.jar

Done!

Go check if you are doing it right:

1. Open CMD
2. type javac, java -version to see if there are something output.

Addictionally, you can set the encoding of JAVA:

• add a new value named JAVA_TOOL_OPTIONS
• set its value as -Dfile.encoding=UTF-8 (or others you need)