Re: do loop bug?
They both are right.
And... one advice:
*Never ever* use exceptions to control normal program flow.
They serve to handle (as name indicates) exceptional situations while
program execution.
This is their purpose. Exception may mean from "this stupid user
entered some text again when was asked to give a numer" up to
"earthquake on the other end of the world destroyed server" ;) , but
it's always something unusual. Exception means that something has gone
wrong.
Next thing: catch exactly exception that is thrown.
If you throw ConnectException, catch this particular exception. This
way you may get some more useful info.
Also: continue (label).
In this code labels are not necessary because (as said before) they
cause jump to while statement in loop being executed. They would be
useful if you wanted to jump somewhere else. But I *strongy recommend*
*not* to do such jumps. They introduce lots of confusion and are likely
to cause a lots of bugs that will be diffult to debug because of hard
to predict program's behaviour. Whenever you want to make such jump,
think twice is there is really no other way.
Try to keep your code as short and simple as possible.
That's my advice. Take it or leave it - it's up to you.
Thea
Mike Schilling napisal(a):
"Patricia Shanahan" <pats@acm.org> wrote in message
news:65wCg.6665$0e5.801@newsread4.news.pas.earthlink.net...
emrefan wrote:
Does this program below indicate to you that there's a bug in java's do
loop. Or is it just one of those many traps that I've fallen into and
I've only got myself to blame? I was expecting the two loops would
behave much the same. Have I been bitten by the optimizer?
public class DoLoopBug {
public static void main( String[] args ) {
int retryCnt = 0;
doLoop1: do {
try {
if (retryCnt < 3)
throw new java.net.ConnectException();
break;
}
catch (Exception e) {
System.out.println( "caught exception; retryCnt=" +
retryCnt );
if (++retryCnt < 20)
continue doLoop1;
}
} while (false);
System.out.println( "after doLoop1, retryCnt = " + retryCnt +
"\n" );
retryCnt = 0;
doLoop2: do {
try {
if (retryCnt < 3)
throw new java.net.ConnectException();
break;
}
catch (Exception e) {
System.out.println( "caught exception; retryCnt=" +
retryCnt );
if (++retryCnt < 20)
continue doLoop2;
}
} while (true); // Here's difference from DoLoop1
System.out.println( "after doLoop2, retryCnt = " + retryCnt );
}
}
The results I get are:
caught exception; retryCnt=0
after doLoop1, retryCnt = 1
caught exception; retryCnt=0
caught exception; retryCnt=1
caught exception; retryCnt=2
after doLoop2, retryCnt = 3
which is what I expected.
Each continue effectively jumps to its loop's while expression
evaluation.
And both "continue"s are unnecessary, since evaluating the "while" is the
next thing to be done anyway, making mw wonder what the intention of the
code is.