Re: Throwing Constructor Exceptions and cleaning up

On Apr 14, 4:02 pm, "Larry K. Wollensham" <lkw4...@xxxxxxxxx> wrote:
Lew wrote:
Another approach puts separate try blocks around things that can fail.

   public MyClass (int arg1) throws IOException
   {
     if (arg1 < 0) throw new IllegalArgumentException();
     InputStream w = new FileInputStream(getFile(arg1));
     assert w != null;
     try
     {
       someSetupStuffThatMayThrow();
     }
     finally
     {
       w.close();
     }
   }

That'll close w no matter what, and doesn't assign it to an instance
variable. If the stream is simply consulted during construction, but
isn't retained open as a part of the object, this makes sense. If it is,
you need the success flag or something similar again so the finally
clause only closes it conditionally, and you need to assign it to
something visible to the rest of the class.

You're right. I should not have gotten rid of the 'success' flag.

What I should have said:

public MyClass (int arg1) throws IOException
{
if (arg1 < 0) throw new IllegalArgumentException();
wrapped = new FileInputStream(getFile(arg1));
assert wrapped != null;
boolean success = false;
try
{
someSetupStuffThatMayThrow();
success = true;
}
finally
{
if ( ! success )
{
wrapped.close();
}
}
}

To get rid of the 'success' variable, have a catch block catch the
exceptions from 'someSetupStuffThatMayThrow()' and close the stream.

public MyClass (int arg1) throws IOException
{
if (arg1 < 0) throw new IllegalArgumentException();
wrapped = new FileInputStream(getFile(arg1));
assert wrapped != null;
try
{
someSetupStuffThatMayThrow();
}
catch ( SetupException exc )
{
final String msg = "setup failed";
logger.error( msg );
try
{
wrapped.close();
}
catch ( IOException ioex )
{
logger.error( "wrapped.close() failed" );
}
throw new IllegalStateException( msg, exc );
}
}

--
Lew
.

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