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.这个处理程序需要分配一个局部变量,见下文.我需要resp在回调中分配并在函数结束时引用它.我在Eclipse中遇到此错误:

resp无法分配最终的局部变量,因为它是在封闭类型中定义的

我怎样才能解决这个问题？

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案例的黑客:

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,如果需要更清晰的解决方案,则必须为处理程序定义命名类,将响应存储在其字段中,并使用访问器方法检索它.

最好的问候,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());
}