用户定义的例外：我们何时使用它们？什么是“例外”情况？ [英] User defined exceptions: when do we use them? What is an "exceptional" situation?

问题描述

我确信这个问题已在许多最佳实践书籍中得到解决，但仍然... ... b $ b大多数时候我看到错误使用自定义异常的例子，因此我想知道什么是使用它们的好情况？

I'm sure that this question has been addressed in many best practices books, but still... Most of the times I see examples of wrong usage of custom exceptions, therefore I was wondering what would be a good situation to use them?

特别是，目前我正在为编译器课程开发类型检查器。因此，我有一个SymbolTable类，它是与普通地图非常相似。与普通地图的主要区别在于每个符号最多只能定义一次，因此如果我们尝试插入的密钥已经存在，则put（String，Object）操作应该会失败SymbolTable。

In particular, at the moment I'm working on a type checker for a compilers course.Therefore, I have a SymbolTable class, which is rather similar to a Map.The key difference from your ordinary map is that each symbol has to be defined at most once, so a put(String, Object) operation should fail if the key we're trying to insert is already present in the SymbolTable.

所以这就是问题：每当我们尝试插入一个密钥，并且该密钥已经存在于SymbolTable中时，SymbolTable应该如何表现？我们应该有一个

So here's the question: whenever we try to insert a key, and that key already exists in the SymbolTable, how should the SymbolTable behave? Should we have a

boolean insert(String key, Object value);

在插入失败的情况下返回false的方法？或者我们应该使用插入方法有一个返回值void并在遇到重复值时抛出异常？

method that returns "false" in case the insert fails?Or should we rather use an insert method that has a return value "void" and throws an exception when a duplicate value is encountered?

提前致谢：）

推荐答案

例外情况应该是特殊情况。

在这种特殊情况下，例如，如果方法名为 insert（）我会将列表密钥上的视为正常情况并更新它。

In that particular case, for example, if method is named insert() I would treat an already on the list key as a normal case and update it.

此外，虽然不应该使用异常来控制代码流，但是返回布尔值指示失败/成功也不是更好的选择（可能有很多情况下失败，False表示什么都没有关于此事。）

Moreover, although exceptions shouldn't be used to control the code flow, return booleans indicating failure/success isn't the better option either(there can be many cases for failure and False indicates nothing on the matter).

底线，我会做一些事情：

Bottom line, I would do something line this:

// Failures can happen 
void add(key, value) throws AlreadyOnMapException

// Update if already on list
void insert(key, value);

// Make available Contains() methods to control the flow by avoiding exceptions
boolean containsKey(key);

boolean containsValue(value);

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