求救~幫忙看一段程式碼是做什麼用的~

    static {
        Runtime runtime = Runtime.getRuntime();
        Class c = runtime.getClass();
        try {
            Method m = c.getMethod("addShutdownHook", new Class[] { Thread.class } );
            m.invoke(runtime, new Object[] { new ShutdownThread() });
        }
        catch (NoSuchMethodException nsme) {
		//do something...
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }