public Timer(boolean isDaemon)
Creates a new timer whose associated thread may be specified to run as a daemon. A daemon thread is called for if the timer will be used to schedule repeating "maintenance activities", which must be performed as long as the application is running, but should not prolong the lifetime of the application.
如果isDaemon为true,那么创建的Timer属于守护线程,应用程序结束之后也会死亡