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
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。
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。
