http://hg.openjdk.java.net/jdk9/jdk9/jdk/file/efbc2dabd84c/src/share/classes/sun/launcher/LauncherHelper.java

399 static String getMainClassFromJar(String jarname) {
      400 String mainValue = null;
      401 try (JarFile jarFile = new JarFile(jarname)) {
      402 Manifest manifest = jarFile.getManifest();
      403 if (manifest == null) {
      404 abort(null, "java.launcher.jar.error2", jarname);
      405 }
      406 Attributes mainAttrs = manifest.getMainAttributes();
      407 if (mainAttrs == null) {
      408 abort(null, "java.launcher.jar.error3", jarname);
      409 }
      410 mainValue = mainAttrs.getValue(MAIN_CLASS);
      411 if (mainValue == null) {
      412 abort(null, "java.launcher.jar.error3", jarname);
      413 }
      414
      415 /*
      416 * Hand off to FXHelper if it detects a JavaFX application
      417 * This must be done after ensuring a Main-Class entry
      418 * exists to enforce compliance with the jar specification
      419 */
      420 if (mainAttrs.containsKey(
      421 new Attributes.Name(FXHelper.JAVAFX_APPLICATION_MARKER))) {
      422 return FXHelper.class.getName();
      423 }
      424
      425 return mainValue.trim();
      426 } catch (IOException ioe) {
      427 abort(ioe, "java.launcher.jar.error1", jarname);
      428 }
      429 return null;
      430 }

Note that FXHelper class is loaded because the static field FXHelper.JAVAFX_APPLICATION_MARKER is referenced. If FX is not used by the app, then the FXHelper class is loaded unnecessarily, thus slowing JVM start-up time and wastes space.

The code should be changed so that the JAVAFX_APPLICATION_MARKER field is moved into the LauncherHelper class. This saves about 4KB of footprint.