跪求！《Java并发编程实战》使用newTaskFor实现线程取消的疑惑求解答！

Question

问题描述在《Java并发编程实战》第7章，作者通过newTaskFor方法封装实现了线程的取消。给出的demo如下：publicabstractclassSocketUsingTaskimplementsCancellableTask{@GuardedBy("this")privateSocketsocket;protectedsynchronizedvoidsetSocket(Sockets){socket=s;}publicsynchronizedvoidcancel(){try{if(socket!=null)socket.close();}catch(IOExceptionignored){}}publicRunnableFuturenewTask(){returnnewFutureTask(this){publicbooleancancel(booleanmayInterruptIfRunning){try{SocketUsingTask.this.cancel();}finally{returnsuper.cancel(mayInterruptIfRunning);}}};}}interfaceCancellableTaskextendsCallable{voidcancel();RunnableFuturenewTask();}@ThreadSafeclassCancellingExecutorextendsThreadPoolExecutor{publicCancellingExecutor(intcorePoolSize,intmaximumPoolSize,longkeepAliveTime,TimeUnitunit,BlockingQueueworkQueue){super(corePoolSize,maximumPoolSize,keepAliveTime,unit,workQueue);}publicCancellingExecutor(intcorePoolSize,intmaximumPoolSize,longkeepAliveTime,TimeUnitunit,BlockingQueueworkQueue,ThreadFactorythreadFactory){super(corePoolSize,maximumPoolSize,keepAliveTime,unit,workQueue,threadFactory);}publicCancellingExecutor(intcorePoolSize,intmaximumPoolSize,longkeepAliveTime,TimeUnitunit,BlockingQueueworkQueue,RejectedExecutionHandlerhandler){super(corePoolSize,maximumPoolSize,keepAliveTime,unit,workQueue,handler);}publicCancellingExecutor(intcorePoolSize,intmaximumPoolSize,longkeepAliveTime,TimeUnitunit,BlockingQueueworkQueue,ThreadFactorythreadFactory,RejectedExecutionHandlerhandler){super(corePoolSize,maximumPoolSize,keepAliveTime,unit,workQueue,threadFactory,handler);}protectedRunnableFuturenewTaskFor(Callablecallable){if(callableinstanceofCancellableTask)return((CancellableTask)callable).newTask();elsereturnsuper.newTaskFor(callable);}}我觉得这段代码有点绕，感觉很不直白，我个人感觉可以换一种方法实现：publicabstractclassSocketUsingTaskextendsFutureTaskimplementsCallable{@GuardedBy("this")privateSocketsocket;protectedsynchronizedvoidsetSocket(Sockets){socket=s;}publicsynchronizedvoidcancel(){try{if(socket!=null)socket.close();}catch(IOExceptionignored){}}@Overridepublicbooleancancel(booleanmayInterruptIfRunning){try{cancel();}finally{returnsuper.cancel(mayInterruptIfRunning);}}}我想知道《Java并发编程实战》中给出的这个demo的最大的优点在哪？为什么要这样实现？因为感觉存在一些多余的操作。谢谢

Answer 1

像这样的类似问题可以提很多，比如ArrayList为什么要继承List接口，直接继承Collection接口也能直接实现软件工程有一些很重要的实践原则，比如开闭原则，决定了你的代码的扩展性如何，一开始不理解是很正常的，都是实践的经验。项目又不是能完成当时的需求即可，还需要考虑的后期的扩展和维护的
                            

Answer 2

我觉得demo的写法有2点：第一demo把Callable重新用CancellableTask扩展了一下，如果你要增加新的功能就可以做到面向接口编程的效果，你直接实现了扩展性肯定没这个好；第二我看newTaskFor那个就是生成RunnableFuture的工厂，这个demo中貌似没有用到