Java options dymysified
JDK_JAVA_OPTIONS is only picked up by the java launcher, so use it for options that you only want to apply (or only make sense for) the java startup command. This variable is also new on JDK 9+, and will be ignored by earlier JDK versions. Hence, it's useful when migrating from older versions to 9+. JAVA_TOOL_OPTIONS is picked up also by other java tools like jar and javac so it should be used for flags that you want to apply (and are valid) to all those java tools.