说明：   定时器 在应用开发中，经常需要一些周期性的操作，比如每5分钟检查一下新邮件等。 对于这样的操作最方便、高效的实现方式就是使用java.util.Timer工具类。
(Timer in application development, often need some periodic operations, such as every 5 minutes to check for new messages and so on. For such operations the most convenient and efficient way to achieve is to use java.util.Timer tools.)