在我们的例子中系统定时器支持回调方法：
1 // This is the SystemTimer implemented by your Operating System (OS) 2 // You don't know how this timer was implemented. This example just 3 // show to you how it could looks like. How you could implement a 4 // callback by yourself if you want to. 5 class SystemTimer { 6 7 List<TimeUpdaterCallBack> callbacks = new ArrayList<TimeUpdaterCallBack>(); 8 9 public void registerCallBackForUpdatesEveryHour(TimeUpdaterCallBack timerCallBack) { 10 callbacks.add(timerCallBack); 11 } 12 13 // ... This SystemTimer may have more logic here we don't know ... 14 15 // At some point of the implementaion of this SystemTimer (you don't know) 16 // this method will be called and every registered timerCallBack 17 // will be called. Every registered timerCallBack may have a totally 18 // different implementation of the method updateTime() and my be 19 // used in different ways by different clients. 20 public void oneHourHasBeenExprired() { 21 22 for (TimeUpdaterCallBack timerCallBack : callbacks) { 23 timerCallBack.updateTime(System.currentTimeMillis()); 24 } 25 } 26 } |
最后是我们虚拟简单的例子中的网站时间更新器：
1 // This is our client. It will be used in our WebSite example. It shall update 2 // the website's time every hour. 3 class WebSiteTimeUpdater { 4 5 public static void main(String[] args) { 6 SystemTimer SystemTimer = new SystemTimer(); 7 TimeUpdaterCallBack webSiteCallBackUpdater = new WebSiteTimeUpdaterCallBack(); 8 SystemTimer.registerCallBackForUpdatesEveryHour(webSiteCallBackUpdater); 9 } 10 } |
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