"Javac" doesn't work correctly on Windows 10
java is part of the JRE, not the JDK.
You need to add the JDK bin to the system PATH, in
"Control Panel" | System | Advanced | "Environment Variables"
After adding C:\Program Files\Java\jdk1.8.0_73\bin to the system variables I turned off my command prompt and opened another one. Then it worked.