在一个catch块中使用多个异常有什么好处？

Question

We've all heard that in Java 7 we can write:

try {
   //something with files and IO
} catch (FileNotFoundException | IOException ex) {
    ex.printStackTrace();
    System.out.println("It's can't copy file");
}

instead of

try {
   //something with files and IO
} catch (FileNotFoundException wx) {
    ex.printStackTrace();
} catch (IOException ex) {
   ex.printStackTrace();
}

but, what is it really good for besides shorter code?
Even if we want the same operations done in each catch block, we can:

1. only catch IOException because FileNotFoundException is a subtype.
   or
2. if one exception is not a subtype of the other one, we can write some handleException() method and call it in each catch block.

So, is this feature only used for cleaner code or for anything else?

Thanks.

Answer 1

It's not for making code look cleaner and saving key strokes. Those are fringe benefits.

Repetition leads to inconsistency and errors. So, by creating a syntax that makes repetition unnecessary, real errors can be avoided. That's the motivation behind DRY—not pretty code that is quicker to write.

Answer 2

是的，它主要用于更清洁的代码。

Answer 3

That idea is equivalent to the difference between:

if (myVar == true && myOtherVar == false)
    // Logic

And

if (myVar == true)
{
    if (myOtherVar == false)
        // Same logic
}

It's just shorter, cleaner code.

Answer 4

It is for cleaner code .. but that is very valuable. In some cases you can have 4 or 5 exceptions thrown and if all you want to do is the same in all cases, which is often the case, that cuts down a lot of code.

This makes it more readable and also better testable. That in itself is valuable enough.

Answer 5

The shorter code means less code for maintenance - that's not so small advantage. Yes, I can write exception-handling method, but now I do not do it so often, eg only when the exception is thrown in different places of code.