The version of Java used to compile REEF is controlled in the Maven pom.xml file in the build plugins section under the maven-compiler-plugin artifact identifier. In order to run REEF applications, you must set the JAVA_HOME environment variable to the correct Java installation directory for your operating system and java version.
On Windows, the JAVA_HOME environment variable is set by the Java installer to $SYSTEM_DRIVE\Program Files\Java\jdk[version number]. You can examine the value of JAVA_HOME on Windows by entering the following command in a powerShell console window.
Java build instructions
C# build instructions