According to the javadoc of

and the methods isPreJavaXX are supposed to

return true if the compiler configuration represents a Java XX compiler or later, false otherwise

The logic within those methods evaluates partially also the parameter source (

) or release ( ) which are completely orthogonal to the javac version being used. They only determine the bytecode version being generated but have nothing to do with the version of the compiler itself.

However I am not sure when CompilerConfiguration.getCompilerVersion() is reliably set at all. IMHO there should be some logic separate for in-process and forked compiling which determines the real javac version (either from system property java.version for in-process compilation or the parsed output of javac -version)