java - Java 中用于 Futures 任务的泛型和通配符

Question

public class SOQuestion {
private class TaskResult1 {//some pojo  
}

private class TaskResult2{// some other pojo 
}

private class Task1 implements Callable<TaskResult1> {
    public TaskResult1 call() throws InterruptedException {
        // do something...
        return new TaskResult1();
    }
}

private class Task2 implements Callable<TaskResult2> {
    public TaskResult2 call() throws InterruptedException {
        // do something else...
        return new TaskResult2();
    }
}

private void cancelFuturesTask1(List<Future<TaskResult1>> futureList ){
    for(Future<TaskResult1> future: futureList){
        if(future.isDone())
        {
            continue;
        } else
        {
            System.out.println("cancelling futures.....Task1.");
            future.cancel(true);
        }
    }
}

private void cancelFuturesTask2(List<Future<TaskResult2>> futureList ){
    for(Future<TaskResult2> future: futureList){
        if(future.isDone())
        {
            continue;
        } else
        {
            System.out.println("cancelling futures.....Task2.");
            future.cancel(true);
        }
    }
}

void runTasks() {
    ExecutorService executor = Executors.newFixedThreadPool(4);
    CompletionService<TaskResult1> completionService1 = new ExecutorCompletionService<TaskResult1>(executor);
    List<Future<TaskResult1>> futuresList1 = new ArrayList<Future<TaskResult1>>();

    for (int i =0 ;i<10; i++) {
        futuresList1.add(completionService1.submit(new Task1()));
    }

    for (int i = 0; i< 10; i++) {
        try {
            Future<TaskResult1> f = completionService1.take();
            System.out.print(f.get());
            System.out.println("....Completed..first one.. cancelling all others.");    
            cancelFuturesTask1(futuresList1);
        } catch (InterruptedException e) {
            System.out.println("Caught interrruption....");
            break;
        } catch (CancellationException e) {
            System.out.println("Cancellation execution....");
            break;
        } catch (ExecutionException e) {
            System.out.println("Execution exception....");
            break;
        }
    }


    CompletionService<TaskResult2> completionService2 = new ExecutorCompletionService<TaskResult2>(executor);
    List<Future<TaskResult2>> futuresList2 = new ArrayList<Future<TaskResult2>>();
    try{
        for (int i =0 ;i<10; i++) {
            futuresList2.add(completionService2.submit(new Task2()));
        }
        for (int i = 0; i< 10; i++) {
            try {
                Future<TaskResult2> f = completionService2.take();
                System.out.print(f.get());
                System.out.println("....Completed..first one.. cancelling all others.");    
                cancelFuturesTask2(futuresList2);
            } catch (InterruptedException e) {
                System.out.println("Caught interrruption....");
                break;
            } catch (CancellationException e) {
                System.out.println("Cancellation execution....");
                break;
            } catch (ExecutionException e) {
                System.out.println("Execution exception....");
                break;
            }
        }
    }catch(Exception e){

    }

    executor.shutdown();
}
}

如示例所示，存在一些重复。我想使用泛型和通配符来概括对象并重用一些方法。

我的具体要求是“cancelFuturesTask1”和“cancelFuturesTask2”。两种方法都做同样的事情。我怎样才能概括它们？ 我读到了这个:https://docs.oracle.com/javase/tutorial/java/generics/subtyping.html

我创建了一个基类“TaskResult”扩展“TaskResult1”和“TaskResult2”

private class TaskResult1 extends TaskResult
private class TaskResult2 extends TaskResult

然后使用

List<Futures<? extends TaskResult>>

这给我带来了复杂的错误，并且我在将概念扩展到List<Futures<?>>时遇到了一些困惑。在这种情况下。 任何有关如何执行此操作的指示或解释都会有所帮助。

提前致谢，如果您需要一些说明，请告诉我。

Answer 1

这对我来说编译得很好，如果您也遇到错误，请告诉我。

public class FutureTest
{

   public void cancelAll( Future<?> ... futures ) {
      for( Future<?> f : futures ) {
         if( !f.isDone() ) {
            Logger.getLogger(FutureTest.class.getName()).log(
                    Level.INFO, "Canceling {0}", f);
            f.cancel(true);
         }
      }
   }

   public <T extends Task1 & Task2> void cancelAll( List<Future<T>> futures ) {
      cancelAll( futures.toArray( new Future[futures.size()]) );
   }
}

interface Task1 {}
interface Task2 {}

更具体的类型，请看我的第二种方法。您可以使用通用方法和有界类型参数来完成此操作，但前提是除一种类型之外的所有类型都是接口(interface)。 Java 不支持多重继承，因此您无法编写一种采用多个(非协变)类类型的方法。这就是为什么我认为像第一个示例这样的无界(通配符，“<?>”)方法在这里更好。

https://docs.oracle.com/javase/tutorial/java/generics/boundedTypeParams.html