局部变量必须是最终的或有效的最终 [英] local variables must be final or effectively final

问题描述

我在Java 8中有一个异步操作，它返回一个onError回调或onSuccess回调。如果操作成功与否，我需要返回我的方法。所以我返回一个布尔值来说明这个信息。我遇到的问题是我得到以下编译错误：

I have an async operation inside of Java 8 which return an onError callback or an onSuccess callback. I need to return inside of my method if the operation was a success or not. So I am returning a boolean to state this information. The problem I am facing is I get the following compilation error:

错误：从内部类引用的局部变量必须是final或
有效最终

error: local variables referenced from an inner class must be final or effectively final

搜索错误我可以看到你不允许这种类型的操作，但是如果操作是否成功？

Googling the error I can see you this type of operation is not allowed, but then how can I return if the operation was a success or not?

 public Boolean addUser(String email, String password) {

    Boolean isSuccess = false;

    Map<String, AttributeValue> item = new HashMap<String, AttributeValue>();
    item.put("email", new AttributeValue(email)); //email
    item.put("password", new AttributeValue(password)); //password

    dynamoDB.putItemAsync(new PutItemRequest().withTableName("Users").withItem(item), new AsyncHandler() {
        @Override
        public void onError(Exception excptn) {

        }

        @Override
        public void onSuccess(AmazonWebServiceRequest rqst, Object result) {
            isSuccess = true;
        }

    });

        return isSuccess;

}

推荐答案

这是不是一个好的做法，也可能不起作用。在您的代码中，新的AsyncHandler（）将在一个单独的线程中运行。由于它不是阻塞调用，因此主线程不会等待它完成。

This is not a good practice and also, it might not work. In your code, new AsyncHandler() will be running in a separate thread. Since it's not a blocking call, main thread will not wait for it's completion.

所以，在调用 dynamoDB.putItemAsync（...）之后会发生什么，返回语句甚至在您的 AsyncHandler（）完成它的执行并更改 isSuccess 的值之前，它将被执行。这意味着， return isSuccess; 可能会返回默认值 false 。

So, what will happen is, just after calling dynamoDB.putItemAsync(...), the return statement will get executed even before your AsyncHandler() finishes it's execution and changes the value of isSuccess. That means, return isSuccess; might return the default value false.

注意：如果您真的想这样做，可以将布尔变量设为 field 变量。

Note: If you really want to do it this way, you can make the boolean variable as a field variable.

public boolean isSuccess = false;

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