我认为只有在无法摆脱当前状态时才应该抛出异常。例如，如果您正在分配内存，但没有任何内存可以分配。在您提到的情况下，您可以清楚地从这些状态中恢复，并相应地将错误代码返回给调用者。

You will see plenty of advice, including in answers to this question, that you should throw exceptions only in "exceptional" circumstances. That seems superficially reasonable, but is flawed advice, because it replaces one question ("when should I throw an exception") with another subjective question ("what is exceptional"). Instead, follow the advice of Herb Sutter (for C++, available in the Dr Dobbs article When and How to Use Exceptions, and also in his book with Andrei Alexandrescu, C++ Coding Standards): throw an exception if, and only if

没有满足先决条件(通常会出现以下情况之一 不可能的)或 替代方案将无法满足后置条件或 替代方案将无法保持不变式。

为什么这样更好呢?它不是用几个关于前置条件，后置条件和不变量的问题代替了这个问题吗?这是更好的几个相关的原因。

Preconditions, postconditions and invariants are design characteristics of our program (its internal API), whereas the decision to throw is an implementation detail. It forces us to bear in mind that we must consider the design and its implementation separately, and our job while implementing a method is to produce something that satisfies the design constraints. It forces us to think in terms of preconditions, postconditions and invariants, which are the only assumptions that callers of our method should make, and are expressed precisely, enabling loose coupling between the components of our program. That loose coupling then allows us to refactor the implementation, if necessary. The post-conditions and invariants are testable; it results in code that can be easily unit tested, because the post-conditions are predicates our unit-test code can check (assert). Thinking in terms of post-conditions naturally produces a design that has success as a post-condition, which is the natural style for using exceptions. The normal ("happy") execution path of your program is laid out linearly, with all the error handling code moved to the catch clauses.

“PasswordNotCorrectException”不是一个使用异常的好例子。用户输入错误的密码是意料之中的，所以在我看来，这几乎不是个例外。您甚至可能从中恢复，显示一个漂亮的错误消息，因此这只是一个有效性检查。

未处理的异常将最终停止执行——这是好事。如果返回false、null或错误代码，则必须自己处理程序的状态。如果您忘记检查某个地方的条件，您的程序可能会继续使用错误的数据运行，并且您可能很难弄清楚发生了什么以及在哪里发生了什么。

当然，空的catch语句也可能导致同样的问题，但至少发现这些语句更容易，而且不需要理解逻辑。

所以根据经验:

在您不想要或无法从错误中恢复的地方使用它们。

我想说，基本上每一个原教旨主义都会导致地狱。

您当然不希望以异常驱动流结束，但是完全避免异常也是一个坏主意。你必须在两种方法之间找到平衡。我不会为每种异常情况创建异常类型。这是没有成效的。

我通常更喜欢创建两种基本类型的异常，它们在整个系统中使用:LogicalException和TechnicalException。如果需要，可以通过子类型进一步区分这些类型，但通常不是没有必要。

技术异常指的是真正意想不到的异常，比如数据库服务器宕机，到web服务的连接抛出IOException等等。

另一方面，逻辑异常用于将不太严重的错误情况传播到上层(通常是一些验证结果)。

请注意，即使是逻辑异常也不是为了定期使用来控制程序流，而是为了突出显示流何时应该真正结束的情况。在Java中使用时，这两种异常类型都是RuntimeException子类，错误处理是高度面向方面的。

因此，在登录示例中，创建类似AuthenticationException的东西并通过枚举值(如UsernameNotExisting、PasswordMismatch等)来区分具体情况可能是明智的。这样就不会产生巨大的异常层次结构，并且可以将捕获块保持在可维护的级别。您还可以轻松地使用一些通用的异常处理机制，因为您已经对异常进行了分类，并且非常清楚要向用户传播什么以及如何传播。

我们的典型用法是，当用户输入无效时，在Web服务调用期间抛出LogicalException。异常被编组到SOAPFault详细信息，然后在客户机上再次被解组到异常，这将导致在某个web页面输入字段上显示验证错误，因为异常已正确映射到该字段。

这当然不是唯一的情况:您不需要点击web服务来抛出异常。你可以在任何特殊情况下自由地这样做(比如在你需要快速失败的情况下)——这都取决于你的判断。

首先，如果API的用户对特定的、细粒度的故障不感兴趣，那么为他们设置特定的异常就没有任何价值。

由于通常不可能知道什么可能对用户有用，一个更好的方法是有特定的异常，但确保它们继承自一个公共类(例如，std::exception或其在c++中的派生类)。这允许您的客户端捕获特定的异常(如果他们愿意的话)，或者捕获更一般的异常(如果他们不关心的话)。

To my mind, the fundamental question should be whether one would expect that the caller would want to continue normal program flow if a condition occurs. If you don't know, either have separate doSomething and trySomething methods, where the former returns an error and the latter does not, or have a routine that accepts a parameter to indicate whether an exception should be thrown if it fails). Consider a class to send commands to a remote system and report responses. Certain commands (e.g. restart) will cause the remote system to send a response but then be non-responsive for a certain length of time. It is thus useful to be able to send a "ping" command and find out whether the remote system responds in a reasonable length of time without having to throw an exception if it doesn't (the caller would probably expect that the first few "ping" attempts would fail, but one would eventually work). On the other hand, if one has a sequence of commands like:

  exchange_command("open tempfile");
  exchange_command("write tempfile data {whatever}");
  exchange_command("write tempfile data {whatever}");
  exchange_command("write tempfile data {whatever}");
  exchange_command("write tempfile data {whatever}");
  exchange_command("close tempfile");
  exchange_command("copy tempfile to realfile");

人们会希望任何操作的失败都能中止整个序列。虽然可以检查每个操作以确保操作成功，但如果命令失败，让exchange_command()例程抛出异常会更有帮助。

实际上，在上面的场景中，有一个参数来选择一些失败处理模式可能会有所帮助:从不抛出异常，仅为通信错误抛出异常，或者在命令没有返回“成功”指示的任何情况下抛出异常。

异常类就像“正常”类。当一个新类“是”一个不同类型的对象，具有不同的字段和不同的操作时，您可以创建一个新类。

As a rule of thumb, you should try balance between the number of exceptions and the granularity of the exceptions. If your method throws more than 4-5 different exceptions, you can probably merge some of them into more "general" exceptions, (e.g. in your case "AuthenticationFailedException"), and using the exception message to detail what went wrong. Unless your code handles each of them differently, you needn't creates many exception classes. And if it does, may you should just return an enum with the error that occured. It's a bit cleaner this way.