Final rethrow in Java: 异常处理

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英文:

Final rethrow in Java: Exception Handling

问题

I was going through some Exception Handling concepts in Java and came across the concept of final rethrow. I read the following article-
https://baptiste-wicht.com/posts/2010/05/better-exception-handling-in-java-7-multicatch-and-final-rethrow.html
Here, its written-
>And the second improvement is a little more complicated. Imagine that you want to catch all exceptions, make several operations and then rethrow it. The code isn't hard to make, but the big problem is that you must add a throws clause to your method signature to manage the new exception launched by your code and this is not the objective. Now, you can do that without adding an exception throws clause :

     // some code
} catch (final Throwable ex) {
     // some more code
    throw ex;
}

>Using the final keyword it allows you to throw an exception of the exact dynamic type that will be throwed. So if an IOException occurs, an IOException will be throwed. Of course, you have to declare the exceptions not caught. You throws clauses will exactly the same if you use the code (in //some code) without catching anything but now you can do something if that happens.

Can somebody please explain what exactly does this mean and what purpose does it solve?

英文:

I was going through some Exception Handling concepts in Java and came across the concept of final rethrow. I read the following article-
https://baptiste-wicht.com/posts/2010/05/better-exception-handling-in-java-7-multicatch-and-final-rethrow.html
Here, its written-
>And the second improvement is a little more complicated. Imagine that you want to catch all exceptions, make several operations and then rethrow it. The code isn't hard to make, but the big problem is that you must add a throws clause to your method signature to manage the new exception launched by your code and this is not the objective. Now, you can do that without adding an exception throws clause :

     // some code
} catch (final Throwable ex) {
     // some more code
    throw ex;
}

>Using the final keyword it allows you to throw an exception of the exact dynamic type that will be throwed. So if an IOException occurs, an IOException will be throwed. Of course, you have to declare the exceptions not caught. You throws clauses will exactly the same if you use the code (in //some code) without catching anything but now you can do something if that happens.

Can somebody please explain what exactly does this mean and what purpose does it solve?

答案1

得分: 1

在Java 6中,这段代码无法编译,你必须将Exception添加到方法签名中:

void m() throws IOException, Exception { ... }

这可以替换为:

void m() throws Exception { ... }

换句话说,如果你想捕获所有异常,编译器会强制你更改方法签名,尽管在这段代码中只有IOException可能会被抛出。

在Java 7中,你可以在不更改方法签名的情况下进行全捕获异常。有关更多信息,请参阅此文章的“Rethrowing Exceptions”部分:https://www.oracle.com/technical-resources/articles/java/java7exceptions.html。

附注:关于final关键字的解释在这个示例中没有真正的区别。

英文:

Imagine this code:

void m() throws IOException {
  try {
    throw new IOException();
  } catch (Exception e) {
    //do something when an exception is thrown...
    throw e;
  }
}

In Java 6, it did not compile and you had to add Exception to the method signature:

void m() throws IOException, Exception { ... }

which can be replaced by

void m() throws Exception { ... }

In other words, if you wanted to catch all exceptions, the compiler forced you to change the method signature, although in this code it is clear that only IOException can be thrown.

The article you link to explains that, in Java 7, you can do a catch-all without changing the method signature.

More information in the "Rethrowing Exceptions" section of this article: https://www.oracle.com/technical-resources/articles/java/java7exceptions.html.

ps: the explanation around the final keyword is wrong, it makes no real difference in this example.

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  • 本文由 发表于 2023年7月6日 22:04:38
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