code: boolean processOldJdk(String jdkHome, Collection<String> classNames) throws IOException {
          String RTJAR = jdkHome + "/jre/lib/rt.jar";
          String CSJAR = jdkHome + "/jre/lib/charsets.jar";
  
          bootClassPath.add(0, new File(RTJAR));
          bootClassPath.add(1, new File(CSJAR));
          options.add("-source");
          options.add("8");
  
          if (classNames.isEmpty()) {
              return doJarFile(RTJAR);
          } else {
              return doClassNames(classNames);
          }
      }
docs: Processes named class files from rt.jar of a JDK version 7 or 8.
  If classNames is empty, processes all classes.
  
  @param jdkHome the path to the "home" of the JDK to process
  @param classNames the names of classes to process
  @return true for success, false for failure
  @throws IOException if an I/O error occurs