Java中的Future和FutureTask有什么区别？

Question

既然使用一个任务ExecutorService可以返回一个，为什么需要使用包装任务和使用方法？我觉得他们都做同样的事情。submit``Callable``Future``FutureTask``Callable``execute

Answer 1

其实你是对的。两种方法是相同的。通常，您不需要自己包装它们。如果是这样，您可能会在AbstractExecutorService中复制代码：

/**
 * Returns a <tt>RunnableFuture</tt> for the given callable task.
 *
 * @param callable the callable task being wrapped
 * @return a <tt>RunnableFuture</tt> which when run will call the
 * underlying callable and which, as a <tt>Future</tt>, will yield
 * the callable's result as its result and provide for
 * cancellation of the underlying task.
 * @since 1.6
 */
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
    return new FutureTask<T>(callable);
}

Future和RunnableFuture之间的唯一区别是run（）方法：

/**
 * A {@link Future} that is {@link Runnable}. Successful execution of
 * the <tt>run</tt> method causes completion of the <tt>Future</tt>
 * and allows access to its results.
 * @see FutureTask
 * @see Executor
 * @since 1.6
 * @author Doug Lea
 * @param <V> The result type returned by this Future's <tt>get</tt> method
 */
public interface RunnableFuture<V> extends Runnable, Future<V> {
    /**
     * Sets this Future to the result of its computation
     * unless it has been cancelled.
     */
    void run();
}

让执行者为您构造FutureTask的一个很好的理由是，确保对FutureTask实例的引用不止一种。也就是说，执行者 拥有 这个实例。