I recently read in a book on a Java-based technology that one can determine if the JDK is installed by running java -version and looking for the the Strings "Client" or "Server" in the output of ...

Is Java installed? To run the Java command, first you must have Java installed. This means either the Java Runtime Environment (JRE) or the full Java Development Kit (JDK).

JAVA_HOME is an operating system environment variable that directs a user to the file system location where the JDK or JRE was installed.