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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.

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5
  • 1
    DRY Commented Aug 25, 2011 at 19:28
  • 1
    So here's a mad question. what happens if want to do an operation for one exception but not the other. eg you want the stack trace of filenotfound but not io. would ex print a stack trace for 2 errors? will there be a way to create multiple exceptions like this catch (FileNotFoundException wx | IOException ex). Note the wx at the end of FileNotFoundException. would you then be able to call different operations on the different exceptions or are you stuck with a one size fits all Commented Aug 25, 2011 at 19:38
  • @OVERTONE - are you sure that you can use it this way? in all the examples ive seen, both exception objects go into one variable. Commented Aug 26, 2011 at 7:46
  • 1
    @dan Thats what I meant. I don't think you can use it this way. I'm not at a machine with java 7 or any of my IDES so I cant check. But I think it would be nice if we had the option to declare multiple seperate exceptions in the same block with this nice syntax. It looks a lot cleaner than having 6-8 catch blocks but if your trying to log a specific exception or do something with it then your out of luck. Commented Aug 26, 2011 at 8:39
  • You could write a handleException function, but: [1] you'd need to pass all relevant information in parameters (making the helper function look more complicated thant it needs to be) and [2] you could not return from the catch, since you'd be inside another function. Commented Oct 13, 2011 at 14:27

5 Answers 5

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10

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.

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3 Comments

Although one could argue that "inconsistency and errors" are eliminated by cleaner code.
Yes, cleaner code is a means to that end (correct code), not the end in itself.
About creating a handleException() method, if we're talking of a method with <=3 lines of code, we may be decreasing readability and increasing boilerplate... Less boilerplate and more readability == cleaner code also
2

Yes, it is primarily for cleaner code.

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1

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.

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1

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, e.g. only when the exception is thrown in different places of code.

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0

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.

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