Avoiding nested try/catch

Question

import java.util.Scanner;

public class Test{

    public static void main(String[] args){

    Scanner input = new Scanner(System.in);
    String str = input.next();
    int a;
    try{
        try{
            a = Integer.parseInt(str);
        }
        catch(NumberFormatException nfe){
            throw new CustomException("message");
        }
        if (a>50) throw new CustomException("message");
    }
    catch(CustomException e){
        //do something
    }
}
}

If str is something other than numbers, parseInt will throw a NumberFormatException. But I want to 'convert' it so that I'll have a CustomException with "message" instead. Can I do this without using a nested try/catch blocks like above?

Is this your exact use case? If so then what you want to do isn't necessary and you can just catch the NumberFormatException. — user1675642, Jul 20 '15 at 08:15
What is your intend? Smells like a [XY-problem](http://meta.stackexchange.com/a/66378). And maybe you can replace the `CustomException` with an [`IllegalArgumentException`](https://docs.oracle.com/javase/8/docs/api/java/lang/IllegalArgumentException.html). — Turing85, Jul 20 '15 at 08:21
Have a look at "exception chaining" before proceeding much further. The answers at the time of my writing this are rubbish. — Bathsheba, Jul 20 '15 at 08:31
@Turing85 err...yeah maybe...but i just wanted to know whether i can rethrow an exception in the catch block and handle the rethrown exception within the method without using a nested try/catch block. — tareviverat, Jul 20 '15 at 14:23

user902383 · Answer 1 · 2015-07-20T08:31:48.813

2

you could refator your example to

 try {
     a = Integer.parseInt(str);
     if (a > 50) {
         throw new CustomException("message");
     }
 } catch (NumberFormatException | CustomException e){
     //do something
 }

edited Jul 20 '15 at 08:31

answered Jul 20 '15 at 08:19

user902383

8,420
8
43
63

2

Your first example doesn't behave the same way as his. You throw a `CustomException` from inside the catch which won't be caught. – Oskar Kjellin Jul 20 '15 at 08:26
when i call System.out.println(e.getMessage()); inside the catch block, a NumberFormatException e will give "For input string: ~~" instead of "message". – tareviverat Jul 20 '15 at 14:27
@tareviverat is it relevant as in both cases you have same message? – user902383 Jul 20 '15 at 14:58
yep, and i'm required to handle with a single method all exceptions thrown, so i need to rethrow a CustomException in the catch block. – tareviverat Jul 20 '15 at 15:22
@tareviverat you don't have to rethrow exception, you could wrap everything in function, and handle exception in shared block in place where you call function – user902383 Jul 21 '15 at 07:47

score 1 · Answer 2 · edited May 23 '17 at 12:21

1

Use the Scanner.hasNextInt() to parse the int without worrying about exceptions.

see this question for detailed code.

edited May 23 '17 at 12:21

Community

1
1

answered Jul 20 '15 at 08:23

Arye Shemesh

582
7
20

score 0 · Answer 3 · answered Jul 20 '15 at 08:20

You could write:

public static void main(String[] args){

    Scanner input = new Scanner(System.in);
    String str = input.next();
    int a;
    try{
        a = Integer.parseInt(str);
        if (a>50) throw new NumberFormatException("message");
    }
    catch(NumberFormatException e){
        //do something
    }
}

but I suggest you to use your version, since the code is more readable. My version, even if removes the inner try, is less readable than yours.

Avoiding nested try/catch

3 Answers3