从内部类访问变量

Question

我有一些代码为回调处理程序定义了一个匿名内部类。该处理程序需要分配一个局部变量，请参见下文。我需要在回调中分配 resp 并在函数末尾引用它。但是，我在 Eclipse 中收到此错误：

无法分配最终局部变量 resp，因为它是在封闭类型中定义的

我该如何解决此问题？

DoorResult unlockDoor(final LockableDoor door) {
    final UnlockDoorResponse resp;
    final boolean sent = sendRequest(new UnlockDoorRequest(door), 
       new ResponseAction() {
        public void execute(Session session) 
               throws TimedOutException, RetryException, RecoverException {
            session.watch(UNLOCK_DOOR);
            resp = (UnlockDoorResponse)session.watch(UNLOCK_DOOR);
        }
    });
    DoorResult result;
    if (!sent) {
        return DoorResult.COMMS_ERROR;
    }
    else {
        return DoorResult.valueOf(resp.getResponseCode());
    }
}

Answer 1

这是一个适用于您的情况的技巧：

DoorResult unlockDoor(final LockableDoor door) {
    final UnlockDoorResponse resp[] = { null };
    final boolean sent = sendRequest(new UnlockDoorRequest(door), new ResponseAction() {
        public void execute(Session session)  throws TimedOutException, RetryException, RecoverException {
            session.watch(UNLOCK_DOOR);
            resp[0] = (UnlockDoorResponse)session.watch(UNLOCK_DOOR);
        }
    });
    DoorResult result;
    if (!sent) {
        return DoorResult.COMMS_ERROR;
    }
    else {
        return null == resp[0] ? null : DoorResult.valueOf(resp[0].getResponseCode());
    }
}

但是，如果您想要一个更清晰的解决方案，则必须为处理程序定义一个命名类，将响应存储在其字段中，并使用访问器方法检索它。

此致，
斯坦.

Answer 2

您可以通过为响应创建一个包装类来解决这个问题。

class ResponseWrapper {
    UnlockDoorResponse resp;
    void setResponse(UnlockDoorResponse resp) {
        this.resp = resp;
    }
    UnlockDoorResponse getResponse() {
        return resp;
    }
}

然后，您的代码将如下所示：

final ResponseWrapper respWrap = new ResponseWrapper();
final boolean sent = sendRequest(new UnlockDoorRequest(door), new ResponseAction() {
    public void execute(Session session)  throws TimedOutException, RetryException, RecoverException {
        session.watch(UNLOCK_DOOR);
        respWrap.setResponse((UnlockDoorResponse)session.watch(UNLOCK_DOOR));
    }
 });
DoorResult result;
if (!sent) {
    return DoorResult.COMMS_ERROR;
}
else {
    return DoorResult.valueOf(respWrap.getResponse().getResponseCode());
}

Answer 3

假设这是您要更改的代码，如何更改 sendRequest 和 ResponseAction.execute 以返回 UnlockDoorResponse 的实例

DoorResult unlockDoor(final LockableDoor door) {
    final UnlockDoorResponse resp = sendRequest(new UnlockDoorRequest(door), new ResponseAction() {
        public UnlockDoorResponse execute(Session session)  throws TimedOutException, RetryException, RecoverException {
            session.watch(UNLOCK_DOOR);
            return (UnlockDoorResponse)session.watch(UNLOCK_DOOR);
        }
    });
    if (resp == null) {
        return DoorResult.COMMS_ERROR;
    }
    else {
        return DoorResult.valueOf(resp.getResponseCode());
    }
}

Answer 4

如果要返回结果，请使用命名内部类而不是匿名内部类。提供的所有其他选项都是恕我直言的丑陋黑客（一个自我承认的；-）

（好吧，@Joel 不是，但假设您可以更改正在实现的接口）

只需创建一个带有结果 getter 的类实例，它就是干净，只需要您实现单个类。

    class MyReponseAction implements ResponseAction {
        private UnlockDoorResponse response; 

        public void execute(Session session)  throws TimedOutException, RetryException, RecoverException {
           session.watch(UNLOCK_DOOR);
           response = (UnlockDoorResponse)session.watch(UNLOCK_DOOR);
        }

        UnlockDoorResponse getResponse() {
            return response;
        }
    }

   DoorResult unlockDoor(final LockableDoor door) {
        ResponseAction action = new MyResponseAction();
        final boolean sent = sendRequest(new UnlockDoorRequest(door), action);

        DoorResult result;
        if (!sent) {
            return DoorResult.COMMS_ERROR;
        }
        else {
            return DoorResult.valueOf(action.getResponse().getResponseCode());
        }
    }