Review

• missing/exception handling

class FSDirectory {
  /** Closes the store to future operations. */
  public synchronized void close() {
    if (--refCount <= 0) {
      synchronized (DIRECTORIES) {
        DIRECTORIES.remove(directory);
      }
    }
  }
}

class FSDirectory.FSIndexInput.Descriptor {
      public void close() throws IOException {
        if (isOpen) {
          isOpen=false;
          super.close();
        }
      }
}

class FSDirectory.FSIndexInput {
    public void close() throws IOException {
      // only close the file if this is not a clone
      if (!isClone) file.close();
    }
}

class FSDirectory.FSIndexOutput {
    public void close() throws IOException {
      // only close the file if it has not been closed yet
      if (isOpen) {
        super.close();
        file.close();
        isOpen = false;
      }
    }

}