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();
}
@ThreadSafe
classCancellingExecutorextendsThreadPoolExecutor{
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();
else
returnsuper.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){}
}
@Override
publicbooleancancel(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