Future接口代表异步计算的结果，并且提供方法来检测异步过程的进展。Callable接口与Runnable接口比较类似，提供线程的执行体，即run方法的内容。

Future与Callable结合使用开启一个新线程执行，最大的特点是能提供返回值，这样也就能实现类似同步执行的情况，看以下示例，在新线程中模拟5s的耗时操作，使用future.get将阻塞等待返回结果。

package demo.thread;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;public class CallableDemo {    public static void main(String[] args) throws InterruptedException,            ExecutionException {        ExecutorService executorService = Executors.newCachedThreadPool();        Future
     
       future = executorService.submit(new Callable
      
       () {            @Override            public String call() throws Exception {                Thread.sleep(5000);                return "future result";            }        });        System.out.println(System.currentTimeMillis());        System.out.println(future.get());        System.out.println(System.currentTimeMillis());    }}
      
     

执行结果如下：

1562077654406

future result

1562077659407

FutureTask间接实现了Runnable和Future接口，同样可以实现上述功能，如下：

package demo.thread;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.FutureTask;public class FutureTaskDemo {    public static void main(String[] args) throws InterruptedException,            ExecutionException {        FutureTask
     
       futureTask = new FutureTask
      
       (                new Callable
       
        () {                    @Override                    public String call() throws Exception {                        Thread.sleep(5000);                        return "future result";                    }                });        new Thread(futureTask).start();        System.out.println(System.currentTimeMillis());        System.out.println(futureTask.get());        System.out.println(System.currentTimeMillis());    }}
       
      
     

执行结果如下：

1562077797983

future result

1562077802985