java - 为最终变量赋值

Question

假设我有这段代码:

public HttpResponse myFunction(...) {
    final HttpResponse resp;
    OnResponseCallback myCallback = new OnResponseCallback() {
        public void onResponseReceived(HttpResponse response) {
            resp = response;
        }
    };
    // launch operation, result will be returned to myCallback.onResponseReceived()
    // wait on a CountDownLatch until operation is finished
    return resp;
}

显然我不能从 onResponseReceived 给 resp 赋值，因为它是一个最终变量，但如果它不是最终变量，onResponseReceived 就看不到它。那么，如何从 onResponseReceived 中为 resp 赋值呢？

我的想法是创建一个包装类来封装resp对象。最终对象将是这个包装类的一个实例，我可以将值分配给在最终类(不是最终类)中处理对象的 resp。

代码应该是这样的:

class ResponseWrapper {
    HttpResponse resp = null;
}

public HttpResponse myFunction(...) {
    final ResponseWrapper respWrap = new ResponseWrapper();
    OnResponseCallback myCallback = new OnResponseCallback() {
        public void onResponseReceived(HttpResponse response) {
            respWrap.resp = response;
        }
    };
    // launch operation, result will be returned to myCallback.onResponseReceived()
    // wait on a CountDownLatch until operation is finished
    return respWrap.resp;
}

您如何看待这个解决方案？

Answer 1

java.util.concurrent.atomic.AtomicReference

标准做法是使用最终的 AtomicReference，您可以设置和获取它。这也增加了线程安全的好处 :) 正如您提到的，CountDownLatch 有助于等待完成。