import java.util.jar.*;

static LS classNamesInJarOrDir(File dir, S prefixInJar default "") {

  new LS classes;

  if (dir == null) {}

  else if (dir.isDirectory()) {

    for (File f : listFiles(dir)) { // TODO: subdirectories

      S s = f.getName();

      if (s.endsWith(".class"))

        classes.add(dropSuffix(".class", s));

    }

  } else if (dir.isFile()) pcall {

    JarFile jarFile = new JarFile(dir);

    try {

      Enumeration<JarEntry> e = jarFile.entries();

      while (e.hasMoreElements()) {

        JarEntry je = e.nextElement();

        if (je.isDirectory()

          || je.getName().startsWith("META-INF/")

          || !je.getName().endsWith(".class"))

          continue;

        S className = dropSuffix(".class", je.getName());

        className = dropPrefixOrNull(prefixInJar, className);

        if (className == null) continue;

        if (className.contains("-")) continue;

        className = className.replace('/', '.');

        classes.add(className);

      }

    } finally {

      jarFile.close();

    }

  }

  ret classes;

}