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Roedy Green - 02 Jul 2005 20:41 GMT

Let's say you have some code like this:

case 1:
if ( x )
if ( y )
return a;
else return b;
else return c;

break;

Jva will insist you take out the break because it is not needed.

then later you inadvertently meddle with the code say like this:

case 1:
if ( x )
if ( y )
return a;
else return c;

now you need the break back in there again, but of course Java wont't
tell you.

What is the best way to handle this to make sure you have covered all
possibilites and that you truly can't ever fall through?

You can't even put debug code in there to catch the problem. Java
will make you take it out if the prgram is CURRENTLY working.

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Raymond DeCampo - 02 Jul 2005 21:54 GMT

> Let's say you have some code like this:
>
[quoted text clipped - 22 lines]
> What is the best way to handle this to make sure you have covered all
> possibilites and that you truly can't ever fall through?

In this case, probably enforcing a one return statement rule.

> You can't even put debug code in there to catch the problem. Java
> will make you take it out if the prgram is CURRENTLY working.

Ray

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Larry Barowski - 02 Jul 2005 22:34 GMT

> Let's say you have some code like this:
>
[quoted text clipped - 25 lines]
> You can't even put debug code in there to catch the problem. Java
> will make you take it out if the prgram is CURRENTLY working.

It's not pretty, but you can always do
if(true)
return x;

I use that all the time to temporarily short-circuit the remainder of a
method for debugging purposes.

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ChrisWSU - 02 Jul 2005 22:47 GMT

with case 1:
if ( x )
if ( y )
return a;
else
return b;
else
return c;
break;

the break; is unreachable... its logically impossible to get to that
line. but with

case 1:
if ( x ) {
if ( y ){
return a;
} else {
return c;
}
}

the case of x being false is not covered so you need a break to keep
from going into next case.

>now you need the break back in there again, >but of course Java wont't
>tell you.

thats because its not supposed to, its part of the switch statement to
allow you to overlap cases, its a feature.

>What is the best way to handle this to make >sure you have covered all
>possibilites and that you truly can't ever fall >through?

truth tables. planning. if switch statements cause to much problems
dont use them. There are alternatives such as if/else ifs. and a few
others that although fun most would consider a kludge :)

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Roedy Green - 02 Jul 2005 23:04 GMT

>thats because its not supposed to, its part of the switch statement to
>allow you to overlap cases, its a feature.

IN my case it as always an error, and one I would like to be informed
of.

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Stefan Schulz - 02 Jul 2005 23:12 GMT

>>thats because its not supposed to, its part of the switch statement to
>>allow you to overlap cases, its a feature.
>
> IN my case it as always an error, and one I would like to be informed
> of.

Why not use

assert false: "Unreachable";

in such a case?

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Roedy Green - 02 Jul 2005 23:24 GMT

>>thats because its not supposed to, its part of the switch statement to
>>allow you to overlap cases, its a feature.
>
>IN my case it as always an error, and one I would like to be informed
>of.

I found what I am looking for a javac.exe switch -Xlint:fallthrough

now to try it out.

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ChrisWSU - 02 Jul 2005 23:46 GMT

oh thats kinda neat, thanx for the follow up

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Tim Tyler - 09 Jul 2005 15:27 GMT

Roedy Green <look-on@mindprod.com.invalid> wrote or quoted:

> What is the best way to handle this to make sure you have covered all
> possibilites and that you truly can't ever fall through?

See:

``FallThrough [...]

Checks for fall through in switch statements Finds locations where a
case contains Java code - but lacks a break, return, throw or continue
statement.''

- http://checkstyle.sourceforge.net/config_coding.html#FallThrough

...and then visit:

http://eclipse-cs.sourceforge.net/

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Joan - 09 Jul 2005 23:57 GMT

> Roedy Green <look-on@mindprod.com.invalid> wrote or quoted:
>
> > What is the best way to handle this to make sure you have covered all
> > possibilites and that you truly can't ever fall through?

Javac version 5.0 has a -X switch that will tell you exactly this.

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