Callable和Future的应用详情

17-12-11 来源：[db:作者]

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Callable和Future这两个组合一起可以实现:
程序启动一个线程,然后线程运行完以后,它可以给我们返回结果

public class CallableAndFuture {

    public static void main(String[] args) {
        ExecutorService threadPool = Executors.newSingleThreadExecutor();
        Future future =   //Future取得的结果类型和Callable返回的结果类型必须一致,这是通过泛型来实现的
        threadPool.submit(new Callable() {//Callable要采用ExecutorSevice的submit方法提交,返回的future对象可以取消任务;这里如果使用execute(Runnable command)方法,则没有返回值
            @Override
            public String call() throws Exception {
                Thread.sleep(2000);
                return "hello";
            }
        });
        System.out.println("等待结果");
        try {
           System.out.println("拿到结果:"+future.get());

        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

    }



}

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public class CallableAndFuture {

    public static void main(String[] args) {
        ExecutorService threadPool = Executors.newSingleThreadExecutor();
        Future future =
        threadPool.submit(new Callable() {
            @Override
            public String call() throws Exception {
                Thread.sleep(2000);
                return "hello";
            }
        });
        System.out.println("等待结果");
        try {

                System.out.println("拿到结果:"+future.get(1, TimeUnit.SECONDS));//没有结果就抛异常


        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        } catch (TimeoutException e) {
            e.printStackTrace();
        }


    }



}

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CompletionService用于提交一组Callable任务,其take方法返回已完成的一个Callable任务对应的Future对象
好比我同时种了几块地的麦子,然后就等待收割。收割时,则是哪块先成熟了,则先去收割哪块麦子

  ExecutorService threadPool2 = Executors.newFixedThreadPool(10);
        CompletionService completionService = new ExecutorCompletionService(threadPool2);
        for(int i = 1 ;i<=10;i++) {
            final int seq = i ;
            completionService.submit(new Callable() {
                @Override
                public Integer call() throws Exception {
                            Thread.sleep(2000);
                    return seq;
                }
            });
        }
        for(int i = 0 ;i<=10;i++){
            try {
                System.out.println(completionService.take().get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }

        }

这里写图片描述

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