关于AsynchronousFileChannel读取数据时CompletionHandler回调函数不执行的问题

[HKxutao]

public class Test144 {
	public static void main(String[] args) {
		Path path = Paths.get("E:/example.txt");
		AsynchronousFileChannel AFC = null;
		try {
			AFC = AsynchronousFileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE);
		} catch (IOException e) {
			e.printStackTrace();
		}
		ByteBuffer BB = ByteBuffer.allocate(64);
		AFC.read(BB, 0, BB, new CompletionHandler<Integer, ByteBuffer>() {
			@Override
			public void completed(Integer result, ByteBuffer attachment) {
				attachment.flip();
				byte[] buf = new byte[attachment.limit()];
				attachment.get(buf);
				System.out.println(new String(buf));
			}

			@Override
			public void failed(Throwable exc, ByteBuffer attachment) {
				System.out.println("error");
			}
		});
	}
}

这个回调函数无法执行，但是当我加入了一个延迟后就执行了，下面是加入延迟后的代码

public class Test144 {
	public static void main(String[] args) throws IOException {
		Path path = Paths.get("E:/example.txt");
		AsynchronousFileChannel AFC = null;
		try {
			AFC = AsynchronousFileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		ByteBuffer BB = ByteBuffer.allocate(64);
		AFC.read(BB, 0, BB, new CompletionHandler<Integer, ByteBuffer>() {
			@Override
			public void completed(Integer result, ByteBuffer attachment) {
				attachment.flip();
				byte[] buf = new byte[attachment.limit()];
				attachment.get(buf);
				System.out.println(new String(buf));
			}

			@Override
			public void failed(Throwable exc, ByteBuffer attachment) {
				System.out.println("error");
			}
		});
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

请问有哪位仁兄为在下解惑？

[HKxutao]

有没有人啊有没有人啊有没有人啊

[hahahuhu_]

因为你的主线程（main）在你的异步线程执行之前退出了，所以你的处理过程是不会显示的控制台上的

[hahahuhu_]

public interface CompletionHandler<V,A>A handler for consuming the result of an asynchronous I/O operation. 

意思是说：CompletionHandler是异步处理的，如果要显示，就要让主线程等一下它

[hahahuhu_]

额，刚才那个不清楚，都跑一行去了。。。

public interface CompletionHandler<V,A>

A handler for consuming the result of an asynchronous I/O operation.