Re: Thumbs up for suppressable exceptions in JDK 1.7

On Tue, 27 Sep 2011, Roedy Green wrote:


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