Re: Thumbs up for suppressable exceptions in JDK 1.7
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
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