Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail
From: Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: Thumbs up for suppressable exceptions in JDK 1.7
Date: Thu, 29 Sep 2011 18:05:09 +0200
Organization: A noiseless patient Spider
Lines: 57
Message-ID: <j6252f$etv$1@dont-email.me>
References: <j5ru3o$cu7$1@news.albasani.net> <cp5387dadnj2jmuheklm82niu718054nsj@4ax.com> <alpine.DEB.2.00.1109272034540.14737@urchin.earth.li>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Injection-Date: Thu, 29 Sep 2011 16:06:39 +0000 (UTC)
Injection-Info: mx04.eternal-september.org; posting-host="AUyBsac4Bvz0HEr1sKU8og"; logging-data="15295"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/Ag2zXjml63EnhDSDbS9sp"
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.2.23) Gecko/20110920 Thunderbird/3.1.15
In-Reply-To: <alpine.DEB.2.00.1109272034540.14737@urchin.earth.li>
Cancel-Lock: sha1:fhs1Pz/N1r5CzNY/Vdb7Ves83Sg=
Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.programmer:8398

On 27/09/2011 21:43, Tom Anderson allegedly wrote:
> On Tue, 27 Sep 2011, Roedy Green wrote:
> 
>> On Tue, 27 Sep 2011 09:31:03 +0200, Jan Burse <janburse@fastmail.fm>
>> wrote, quoted or indirectly quoted someone who said :
>>
>>> Was just playing around with suppressable exceptions in JDK 1.7. This
>>> looks like a great improvement for bug hunting!
>>>         ... 5 more
>>
>> I think you need some exposition on why this is a good thing.
> 
> It avoids this common mistake:
> 
> try {
>     doSomethingWhichMightThrowAnException();
> }
> finally {
>     doSomeCleanupWhichMightThrowAnException();
> }
> 
> In that code, if both methods throw an exception, you will only see the
> second. The first exception - the one which actually caused the problem
> - will be lost. It's as if the VM has a very short attention span, and
> can only focus on whatever exception was most recently thrown.
> 
> In Java 7, you can put the cleanup into the close() method of an
> (Auto)Closeable, and use the try-with-resources form:
> 
> class Thing implements AutoCloseable {
>     public void close() throws AnException {
>         doSomeCleanupWhichMightThrowAnException();
>     }
> }
> 
> try (Thing t = new Thing()) {
>     doSomethingWhichMightThrowAnException();
> }
> 
> There, the compiler will arrange things so that if close() does throw an
> exception, it will be 'suppressed', and tagged on to the exception
> coming from doSomethingWhichMightThrowAnException() as a suppressed
> exception.
> 
> tom
> 

Indeed, but even more generally, we can from now on register
"suppressed" exceptions ourselves, as Jan's code and the JSE7 Javadoc
for java.lang.Throwable show. Great Thing IMHO. Closes a hole that's
been lurking there for a very long time.

Thanks Jan for bringing this to my attention.

-- 
DF.
Determinism trumps correctness.