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
１ ． 如果你不确定一个异常，检查API:
java . lang . object
由java.lang.Throwable扩展
由java.lang.Exception扩展
//<-NumberFormatException是一个RuntimeException
由java.lang.IllegalArgumentException扩展
由java.lang.NumberFormatException扩展
2。是的，以及所有扩展它的异常。
3.不需要捕获和抛出相同的异常。在这种情况下，您可以显示一个新的文件对话框。
4所示。FileNotFoundException已经是一个检查异常。
5。如果期望调用someMethod的方法捕获异常，则可以抛出后者。它只是“传球”。使用它的一个例子是，如果你想在你自己的私有方法中抛出它，而在你的公共方法中处理异常。
一个很好的阅读是Oracle文档本身:http://download.oracle.com/javase/tutorial/essential/exceptions/runtime.html
Why did the designers decide to force a method to specify all uncaught checked exceptions that can be thrown within its scope? Any Exception that can be thrown by a method is part of the method's public programming interface. Those who call a method must know about the exceptions that a method can throw so that they can decide what to do about them. These exceptions are as much a part of that method's programming interface as its parameters and return value.
The next question might be: "If it's so good to document a method's API, including the exceptions it can throw, why not specify runtime exceptions too?" Runtime exceptions represent problems that are the result of a programming problem, and as such, the API client code cannot reasonably be expected to recover from them or to handle them in any way. Such problems include arithmetic exceptions, such as dividing by zero; pointer exceptions, such as trying to access an object through a null reference; and indexing exceptions, such as attempting to access an array element through an index that is too large or too small.
在Java语言规范中还有一些重要的信息:
在throws子句中命名的受控异常类是方法或构造函数的实现者和用户之间契约的一部分。
IMHO的底线是，您可以捕获任何RuntimeException，但不需要这样做，事实上，实现不需要维护抛出的相同的未检查异常，因为这些异常不是契约的一部分。
我只是想添加一些根本不使用受控异常的理由。这不是一个完整的答案，但我觉得它确实回答了你的部分问题，并补充了许多其他的答案。
Whenever checked exceptions are involved, there's a throws CheckedException somewhere in a method signature (CheckedException could be any checked exception). A signature does NOT throw an Exception, throwing Exceptions is an aspect of implementation. Interfaces, method signatures, parent classes, all these things should NOT depend on their implementations. The usage of checked Exceptions here (actually the fact that you have to declare the throws in the method signature) is binding your higher-level interfaces with your implementations of these interfaces.
让我给你们看一个例子。
让我们有一个像这样漂亮干净的界面
public interface IFoo {
public void foo();
}
现在我们可以编写方法foo()的许多实现，就像这样
public class Foo implements IFoo {
@Override
public void foo() {
System.out.println("I don't throw and exception");
}
}
类Foo完全没问题。现在让我们第一次尝试Bar类
public class Bar implements IFoo {
@Override
public void foo() {
//I'm using InterruptedExcepton because you probably heard about it somewhere. It's a checked exception. Any checked exception will work the same.
throw new InterruptedException();
}
}
这个类Bar不能编译。由于InterruptedException是一个已检查异常，您必须捕获它(在方法foo()中使用try-catch)或声明您正在抛出它(在方法签名中添加抛出InterruptedException)。因为我不想在这里捕获这个异常(我希望它向上传播，这样我就可以在其他地方正确地处理它)，让我们改变签名。
public class Bar implements IFoo {
@Override
public void foo() throws InterruptedException {
throw new InterruptedException();
}
}
这个类Bar也不能编译!Bar的方法foo()不会覆盖IFoo的方法foo()，因为它们的签名不同。我可以删除@Override注释，但我想编程接口IFoo像IFoo foo;然后再决定使用哪个实现，比如foo = new Bar();如果Bar的方法foo()没有覆盖IFoo的方法foo，当我执行foo.foo();它不会调用Bar的foo()实现。
To make Bar's public void foo() throws InterruptedException override IFoo's public void foo() I MUST add throws InterruptedException to IFoo's method signature. This, however, will cause problems with my Foo class, since it's foo() method's signature differs from IFoo's method signature. Furthermore, if I added throws InterruptedException to Foo's method foo() I would get another error stating that Foo's method foo() declares that it throws an InterruptedException yet it never throws an InterruptedException.
正如您所看到的(如果我在解释这些东西方面做得不错的话)，抛出InterruptedException这样的检查异常的事实迫使我将我的接口IFoo绑定到它的一个实现上，这反过来又会对IFoo的其他实现造成严重破坏!
这就是受控异常很糟糕的一个重要原因。在帽。
一种解决方案是捕获已检查异常，将其包装在未检查的异常中，然后抛出未检查的异常。
这里有一个简单的规则可以帮助你做出决定。它与Java中如何使用接口有关。
以你的类为例，想象一下为它设计一个接口，该接口描述类的功能，但不描述底层实现(接口应该这样)。假设您可能以另一种方式实现该类。
查看接口的方法，并考虑它们可能抛出的异常:
如果方法可以抛出异常，而不管底层实现是什么(换句话说，它只描述功能)，那么它可能应该是接口中的受控异常。
如果异常是由底层实现引起的，那么它不应该出现在接口中。因此，它必须是类中的未检查异常(因为未检查异常不需要出现在接口签名中)，或者必须将其包装并作为接口方法的一部分的已检查异常重新抛出。
To decide if you should wrap and rethrow, you should again consider whether it makes sense for a user of the interface to have to handle the exception condition immediately, or the exception is so general that there is nothing you can do about it and it should propagate up the stack. Does the wrapped exception make sense when expressed as functionality of the new interface you are defining or is it just a carrier for a bag of possible error conditions that could also happen to other methods? If the former, it might still be a checked exception, otherwise it should be unchecked.
通常不应该计划“冒泡”异常(捕获并重新抛出)。异常要么应该由调用者处理(在这种情况下它被检查)，要么应该一直向上到高级处理程序(在这种情况下，如果它不被检查是最简单的)。
