只有在确实是错误时才抛出异常。如果对象不存在是预期行为，则返回null。

否则就是个人喜好的问题了。

作为一般规则，如果方法应该总是返回一个对象，那么就使用例外。如果您预期偶尔会出现null，并希望以某种方式处理它，那么就使用null。

无论你做什么，我强烈建议反对第三种选择:返回一个字符串，说“WTF”。

这取决于你是否希望找到这个物体。如果你遵循学校的思想，认为exceptions应该用来表示某事，那么，嗯，呃，exceptions已经发生了:

对象发现;返回对象 没有找到对象;抛出异常

否则，返回null。

只提到null不被认为是异常行为的情况，我肯定是try方法，很明显，没有必要“阅读书籍”或“三思而后行”，就像这里所说的那样

所以:

bool TryFindObject(RequestParam request, out ResponseParam response)

这意味着用户的代码也将是清晰的

...
if(TryFindObject(request, out response)
{
  handleSuccess(response)
}
else
{
  handleFailure()
}
...

如果方法返回一个集合，则返回一个空集合(如上所述)。但请不要收钱。EMPTY_LIST或类似的!(以Java为例)

如果该方法检索单个对象，则您有一些选项。

If the method should always find the result and it's a real exception case not to find the object, then you should throw an exception (in Java: please an unchecked Exception) (Java only) If you can tolerate that the method throws a checked exception, throw a project specific ObjectNotFoundException or the like. In this case the compiler says you if you forget to handle the exception. (This is my preferred handling of not found things in Java.) If you say it's really ok, if the object is not found and your Method name is like findBookForAuthorOrReturnNull(..), then you can return null. In this case it is strongly recomminded to use some sort of static check or compiler check, wich prevents dereferencing of the result without a null check. In case of Java it can be eg. FindBugs (see DefaultAnnotation at http://findbugs.sourceforge.net/manual/annotations.html) or IntelliJ-Checking.

如果决定返回null，请小心。如果你不是项目中唯一的程序员，你会在运行时得到nullpointerexception(在Java或其他语言中)!所以不要返回在编译时没有检查的空值。

抛出异常的好处:

Cleaner control flow in your calling code. Checking for null injects a conditional branch which is natively handled by try/catch. Checking for null doesn't indicate what it is you're checking for - are you checking for null because you're looking for an error you're expecting, or are you checking for null so you don't pass it further on downchain? Removes ambiguity of what "null" means. Is null representative of an error or is null what is actually stored in the value? Hard to say when you only have one thing to base that determination off of. Improved consistency between method behavior in an application. Exceptions are typically exposed in method signatures, so you're more able to understand what edge cases the methods in an application account for, and what information your application can react to in a predictable manner.

有关更多示例的解释，请参见:http://metatations.com/2011/11/17/returning-null-vs-throwing-an-exception/