约书亚·布洛赫在《有效的Java》中说过
为以下情况使用检查异常
可恢复条件和运行时
编程错误的例外
(第二版第58项)
看看我理解的对不对。
以下是我对受控异常的理解:
try{
String userInput = //read in user input
Long id = Long.parseLong(userInput);
}catch(NumberFormatException e){
id = 0; //recover the situation by setting the id to 0
}
1. 上述异常是否被认为是受控异常?
2. RuntimeException是未检查的异常吗?
以下是我对未检查异常的理解:
try{
File file = new File("my/file/path");
FileInputStream fis = new FileInputStream(file);
}catch(FileNotFoundException e){
//3. What should I do here?
//Should I "throw new FileNotFoundException("File not found");"?
//Should I log?
//Or should I System.exit(0);?
}
4. 现在，上面的代码不能也是一个受控异常吗?我可以试着挽回这样的局面吗?我可以吗?(注:我的第三个问题在上面的陷阱里)
try{
String filePath = //read in from user input file path
File file = new File(filePath);
FileInputStream fis = new FileInputStream(file);
}catch(FileNotFoundException e){
//Kindly prompt the user an error message
//Somehow ask the user to re-enter the file path.
}
5. 人们为什么要这样做?
public void someMethod throws Exception{
}
为什么他们让异常冒出来?早点处理错误不是更好吗?为什么要冒出来?
6. 我是否应该冒泡出确切的异常或使用异常掩盖它?
以下是我的阅读资料
在Java中，什么时候应该创建检查异常，什么时候应该是运行时异常?
何时选择已检查异常和未检查异常
许多人说检查异常(即你应该显式地捕获或重新抛出的异常)根本不应该使用。例如，它们在c#中被淘汰了，大多数语言都没有它们。因此，您总是可以抛出RuntimeException的子类(未检查的异常)
然而，我认为受控异常是有用的——当你想强迫API的用户思考如何处理异常情况(如果它是可恢复的)时，就使用它们。只是受控异常在Java平台中被过度使用了，这让人们讨厌它们。
以下是我对这个话题的扩展观点。
关于具体问题:
Is the NumberFormatException consider a checked exception?
No. NumberFormatException is unchecked (= is subclass of RuntimeException). Why? I don't know. (but there should have been a method isValidInteger(..))
Is RuntimeException an unchecked exception?
Yes, exactly.
What should I do here?
It depends on where this code is and what you want to happen. If it is in the UI layer - catch it and show a warning; if it's in the service layer - don't catch it at all - let it bubble. Just don't swallow the exception. If an exception occurs in most of the cases you should choose one of these:
log it and return
rethrow it (declare it to be thrown by the method)
construct a new exception by passing the current one in constructor
Now, couldn't the above code also be a checked exception? I can try to recover the situation like this? Can I?
It could've been. But nothing stops you from catching the unchecked exception as well
Why do people add class Exception in the throws clause?
Most often because people are lazy to consider what to catch and what to rethrow. Throwing Exception is a bad practice and should be avoided.
遗憾的是，没有单一的规则可以让您决定何时捕获、何时重新抛出、何时使用已检查异常和何时使用未检查异常。我同意这会导致很多混乱和很多糟糕的代码。布洛赫阐述了总体原则(你引用了其中的一部分)。一般的原则是将异常重新抛出到可以处理它的层。
