assert（false）vs RuntimeException？ [英] assert(false) vs RuntimeException?

问题描述

我正在阅读 XWalkUIClientInternal ，我遇到了以下代码：

I'm reading the source of XWalkUIClientInternal and I ran into the following code:

    switch(type) {
        case JAVASCRIPT_ALERT:
            return onJsAlert(view, url, message, result);
        case JAVASCRIPT_CONFIRM:
            return onJsConfirm(view, url, message, result);
        case JAVASCRIPT_PROMPT:
            return onJsPrompt(view, url, message, defaultValue, result);
        case JAVASCRIPT_BEFOREUNLOAD:
            // Reuse onJsConfirm to show the dialog.
            return onJsConfirm(view, url, message, result);
        default:
            break;
    }
    assert(false);
    return false;

我从来没有真正看到这种技术，也没有真正考虑过，但我猜这本质上是这是不可达到的代码，不应该发生，无论什么都崩溃了。虽然技术上你可以做一个Throwable，只要它没有被捕获。

I've never really seen this technique nor really thought about it before, but I guess this essentially means "this is unreachable code and should not happen ever", and crash the app no matter what. Although technically you can do that with a Throwable, as long as it's not caught.

所以我的问题是，哪一个更好，为什么， assert（false）或抛出一个 RuntimeException ，或者可能是一个错误？

So my question is, which one is better and why, assert(false) or throwing a RuntimeException, or maybe an Error?

推荐答案

assert false;

（不需要括号，断言不是一个函数，而是一个语句。）和

(The parenthesis are not needed, assert is not a function but a statement.) and

throw new RuntimeException();

是断言可以被禁用。实际上，除非JVM以 -ea （enable assertions）标志开始，否则 将被禁用。如果断言被启用， assert false 将无条件地抛出一个 AssertionError ，它来源于错误。但是，由于断言可以被禁用，所以有两个问题，

is that the assertion can be disabled. Actually, it is disabled by default unless the JVM is started with the -ea ("enable assertions") flag. If assertions are enabled, assert false will unconditionally throw an AssertionError which derives from Error. But since assertions can be disabled, there are two problems,

• 错误可能未被检测到，

断言（这主要是混乱的）之后的一个虚拟的返回语句。

• the error might go undetected and
• control flow analysis requires a dummy return statement after the assert (which is mostly clutter).

因此，在上述情况下，我一定会明确（而且更简洁）

Therefore, in the above case, I'd certainly go with an explicit (and more concise)

throw new AssertionError("invalid type " + type);

而不是一个断言 返回。

如评论中所述，这是假设类型是内部参数，无效值表示逻辑本身的错误。如果它是一个输入参数，它应该根据通常的规则进行验证，并且 IllegalArgumentException 如果验证失败，则抛出

As mentioned in the comments, this is assuming that type is an internal parameter and an invalid value indicates a bug in the logic itself. If it is an input parameter, it should be validated according to the usual rules and an IllegalArgumentException be thrown if validation fails.

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