线程池执行Future的值为什么是null？

Question

     ExecutorService executorService;
    executorService = new ThreadPoolExecutor(3,5,4,
            TimeUnit.SECONDS,new ArrayBlockingQueue<>(5),Executors.defaultThreadFactory(),
            new ThreadPoolExecutor.AbortPolicy());


    System.out.println(executorService.submit(new FutureTask<String>(new Callable<String>() {
        @Override
        public String call() throws Exception {
            return "aa";
        }
    })).get());

代码如上，请问为什么控制台打印的的值为null呢？

Answer 1

代码修改如下:

public class FieldMethodTest {
    public static void main(String[] args) throws Exception{
        ExecutorService executorService;
        executorService = new ThreadPoolExecutor(3,5,4,
                TimeUnit.SECONDS,new ArrayBlockingQueue<>(5), Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.AbortPolicy());
        Future<String> submit = executorService.submit(new Callable<String>() {
            @Override
            public String call() throws Exception {
                return "aa";
            }
        });
        System.out.println(submit.get());
    }
}