Java中的Runnable，Callable，Future，FutureTask的比较
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2020-08-31
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Java中的中的Runnable，，Callable，，Future，，FutureTask的比较的比较
主要介绍了Java中的Runnable，Callable，Future，FutureTask的比较的相关资料,需要的朋友可以参考下
Java中的中的Runnable，，Callable，，Future，，FutureTask的比较的比较
Java中存在Runnable、Callable、Future、FutureTask这几个与线程相关的类或者接口，在Java中也是比较重要的几个概
念，我们通过下面的简单示例来了解一下它们的作用于区别。
Runnable
其中Runnable应该是我们最熟悉的接口，它只有一个run()函数，用于将耗时操作写在其中， 该函数没有返回值 。然后使用某
个线程去执行该runnable即可实现多线程，Thread类在调用start()函数后就是执行的是Runnable的run()函数。Runnable的声
明如下 :
@FunctionalInterface
public interface Runnable {
/**
* When an object implementing interface <code>Runnable</code> is used
* to create a thread, starting the thread causes the object's
* <code>run</code> method to be called in that separately executing
* thread.
* <p>
* The general contract of the method <code>run</code> is that it may
* take any action whatsoever.
*
* @see java.lang.Thread#run()
*/
public abstract void run();
}
Callable
Callable与Runnable的功能大致相似，Callable中有一个call()函数，但是 call()函数有返回值 ，而Runnable的run()函数不能将
结果返回给客户程序。Callable的声明如下 :
@FunctionalInterface
public interface Callable<V> {
/**
* Computes a result, or throws an exception if unable to do so.
*
* @return computed result
* @throws Exception if unable to compute a result
*/
V call() throws Exception;
}
可以看到，这是一个泛型接口，call()函数返回的类型就是客户程序传递进来的V类型。
Future
Executor就是Runnable和Callable的调度容器，Future就是对于具体的Runnable或者Callable任务的执行结果进行取消、查询
是否完成、获取结果、设置结果操作。get方法会阻塞，直到任务返回结果(Future简介)。Future声明如下:
* @see FutureTask
* @see Executor
* @since 1.5
* @author Doug Lea
* @param <V> The result type returned by this Future's {@code get} method
*/
public interface Future<V> {
/**
* Attempts to cancel execution of this task. This attempt will
* fail if the task has already completed, has already been cancelled,
* or could not be cancelled for some other reason. If successful,
* and this task has not started when {@code cancel} is called,
* this task should never run. If the task has already started,
* then the {@code mayInterruptIfRunning} parameter determines
* whether the thread executing this task should be interrupted in
* an attempt to stop the task.
*
* <p>After this method returns, subsequent calls to {@link #isDone} will
* always return {@code true}. Subsequent calls to {@link #isCancelled}
* will always return {@code true} if this method returned {@code true}.
*
* @param mayInterruptIfRunning {@code true} if the thread executing this
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