If a version of Java has been installed by the user, its version number can be checked by typing java -version on the command line, the output of which should look something like this:
java version "1.8.0_271" Java(TM) SE Runtime Environment (build 1.8.0_271-b09) Java HotSpot(TM) 64-Bit Server VM (build 25.271-b09, mixed mode)The number that follows the underscore refers to the update of the Java version that has been installed. When reporting a problem with the OT, the full version number including the update should be reported.
It may be possible to work with two different user-installed versions of Java (i.e. 8 and 11) and switching between these.
Note for MacOS Users: Apple has introduced a security measure which makes it difficult to install unsigned software. Therefore we recommend the some steps in Sec. 2.2.1 to ensure that the correct version of Java is installed.