Callable与Future

本文可作为传智播客《张孝祥-Java多线程与并发库高级应用》的学习笔记。

在前面写的代码中,所有的任务执行也就执行了,run方法的返回值为空。

java.util.concurrent Interface Callable<V>

public class FutureTask<V> extends Object implements RunnableFuture<V>

使用FutureTask

public static void main(String[] args) {
        Callable<Integer> callable = new Callable<Integer>() {  
            public Integer call() throws Exception {  
                int a=new Random().nextInt(100);
                System.out.println(a+"   ss");
                return a;  
            }  
        };  
        
        FutureTask<Integer> ft=new FutureTask<Integer>(callable);
//        for (int i = 0; i < 5; i++)
//            new Thread(ft).start();
    
        new Thread(ft).start();

        try {
            System.out.println("得到结果 "+ft.get());
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ExecutionException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

我们再看看Future类

使用线程池

public static void main(String[] args) {
    ExecutorService threadPool =  Executors.newSingleThreadExecutor();
    Future<String> future =
        threadPool.submit(
            new Callable<String>() {
                public String call() throws Exception {
                    Thread.sleep(2000);
                        return "hello";
                };
            }
    );
    System.out.println("等待结果");
    //这里应该有trycatch
    System.out.println("拿到结果：" + future.get());
}

多个任务

public static void main(String[] args) {
        
        ExecutorService threadPool2 =  Executors.newFixedThreadPool(10);
        CompletionService<Integer> completionService = new ExecutorCompletionService<Integer>(threadPool2);
        for(int i=1;i<=10;i++){
            final int seq = i;
            completionService.submit(new Callable<Integer>() {
                @Override
                public Integer call() throws Exception {
                    Thread.sleep(new Random().nextInt(5000));
                    return seq;
                }
            });
        }
        for(int i=0;i<10;i++){
            System.out.println(completionService.take().get());
            //上面本应该有trycatch
        }
        threadPool2.shutdown();

    }

3
9
1
6
8
4
7
10
5
2

completionService.submit了10个任务,completionService本身也不知道那个任务先执行完。completionService.take()就是获得已经执行完的那个任务的Future。

感谢glt

参考资料

Callable与Future

原文：http://blog.csdn.net/dlf123321/article/details/42984985