{- -------------------------------------------
  (1) 新しい ReferenceHandler クラスのインスタンスを生成し. Thread.start() で実行を開始させる.
      ---------------------------------------- -}

        static {
            ThreadGroup tg = Thread.currentThread().getThreadGroup();
            for (ThreadGroup tgn = tg;
                 tgn != null;
                 tg = tgn, tgn = tg.getParent());
            Thread handler = new ReferenceHandler(tg, "Reference Handler");
            /* If there were a special system-only priority greater than
             * MAX_PRIORITY, it would be used here
             */
            handler.setPriority(Thread.MAX_PRIORITY);
            handler.setDaemon(true);
            handler.start();
        }