get(long timeout, TimeUnit unit)用来获取执行结果,如果在指定时间内,还没获取到结果,就直接返回null。

而FutureTask即可以作为Runnable又可以作为Future,这样就既可以用ExecutorService的execute执行任务,也可以用ExecutorService的submit提交任务。

例子1:

Callable、Future实现子线程执行任务,并返回结果,主线程等待子线程结果在进行其他逻辑。(多个子线程并行执行任务,主线程做合并处理参见CompletionService用法 )

Callable、Future和FutureTask使用说明_import

 1 import java.util.concurrent.Callable; 2 import java.util.concurrent.ExecutionException; 3 import java.util.concurrent.ExecutorService; 4 import java.util.concurrent.Executors; 5 import java.util.concurrent.Future; 6   7 public class CallableAndFuture1 { 8   9         public static void main(String[] args) {10               ExecutorService service = Executors.newSingleThreadExecutor();11  12               Future<Integer> future = service.submit( new Callable<Integer>() {13  14                       @Override15                       public Integer call() throws Exception {16                            System. out.println("子线程" + Thread.currentThread().getName() + "在进行计算");17                            Thread. sleep(3000);18  19                             int sum = 0;20                             for (int i = 0; i < 100; i++) {21                                   sum += i;22                            }23                             return sum;24                      }25               });26  27               System. out.println("主线程" + Thread.currentThread ().getName() + "在执行任务" );28  29                try {30                      System. out.println("子线程运行结果" + future.get());31               } catch (InterruptedException e) {32                      e.printStackTrace();33               } catch (ExecutionException e) {34                      e.printStackTrace();35               }36  37               System. out.println("所有任务执行完毕" );38  39        }40 }

Callable、Future和FutureTask使用说明_import