""Do not use exceptions for flow control", huh?

[Simon Cockayne]

Hi Kathy and Bert,

With reference to the Java 2 (Sun certified programmer and developer):

Chapter 4, page 212:

"...Java also throws in a couple of flow control features you might not have used before - exceptions and assertions."

Chapter 12, page 599:

"Do not use exceptions for flow control!"


These two statements appear to be at odds with each other.


Please can you clarify, perhaps giving an example of what NOT to do?


Regards,

Simon

[Barry Gaunt]

An obvious example of misuse of exceptions:

public class Baddy
{
    public static void main(String[] args) {
        int[] a = {1, 2, 3, 4, 5};
        int c = 0;
        for (int i = 0; true; )
        try {
            System.out.println(a[i++]);
            c++;
        }
        catch (ArrayIndexOutOfBoundsException e ){
            System.out.println("array length " + c);
            break;
        }
    }
}
    

Perhaps the first sentence would have been better as:
"There are two other Java features that can affect the flow of control: assertions and exceptions. However, they should never be used to expicitly control the flow of execution except in the ways that they are intended to be used. That is, to handle exceptional circumstances arising in your program."

[Jeroen T Wenting]

Exceptions and assertions can be used for flow control, but should not be so used, at least not for flow control in normal program execution.
Both are meant purely for flow control in abnormal program execution, in other words for error handling.

[Simon Cockayne]

Thanks Barry good example.

Cheers Jeroen.