Path: csiph.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: v_borchert@despammed.com (Volker Borchert)
Newsgroups: comp.lang.java.programmer
Subject: Re: How to handle same sanity checks
Date: 22 Jun 2017 18:33:15 GMT
Organization: Private site at Eddersheim, Germany
Lines: 61
Distribution: world
Message-ID: <oih2hb$bad$1@Gaia.teknon.de>
References: <87o9tgo0a9.fsf@munus.decebal.nl> <oiga3s$jrd$1@dont-email.me>
X-Trace: individual.net 3Pumc/2VrhtzhQN0wyq5wADxVuEPp7wqoHEEvCrUMFJSujnTna
Cancel-Lock: sha1:eJQqk6dAWtk09aiZrSG4lCqe1rs=
Xref: csiph.com comp.lang.java.programmer:36700

Eric Sosman wrote:
> On 6/22/2017 5:10 AM, Cecil Westerhof wrote:
> > In my code I have several methods that start with:
> >      if ((n < MIN_VAL) || (n > MAX_VAL)) {
> >          throw new InvalidParameterException(String.format(ERROR_N, n));
> >      }
> > 
> > That is not really DRY.
> > 
> > I could write a method like:
> >      private void checkN(n) {
> >          if ((n < MIN_VAL) || (n > MAX_VAL)) {
> >              throw new InvalidParameterException(String.format(ERROR_N, n));
> >          }
> >      }
> > 
> > And then replace all the checks with a call to checkN. But then the
> > exception is generated in the method checkN instead of the method that
> > has a wrong parameter.
> > What is the best way to handle this?
> 
>      Tastes surely vary, but for repetitive checks I favor writing
> the private internal helper method.  Yes, the caller of doItPlease()
> gets an exception originating from internalSanityCheck() instead, but
> that shouldn't bother anyone.  doItPlease() will be in the stack
> trace anyhow, even though it's not at the very top.

That can be a problem with some more-or-less-broken logging frameworks,
and a nuisance if trying to diagnose over the phone.

You can always do something like

	final InvalidParameterException e
	  = new InvalidParameterException(String.format(ERROR_N, n));
	final StackTraceElement[] s = e.getStackTrace();
	e.setStackTrace(Arrays.copyOfRange(s, 1, s.length));
	throw e;

or even

public class Throwables {
	private Throwables() {
	}

	public static <T extends Throwable> T relocate(final T t, final int n) {
		final StackTraceElement[] s = t.getStackTrace();
		if (n < s.length) {
			t.setStackTrace(Arrays.copyOfRange(s, n, s.length));
		}
		return t;
	}
}

and then

	throw Throwables.relocate(new InvalidParameterException(...)), 1);

-- 

"I'm a doctor, not a mechanic." Dr Leonard McCoy <mccoy@ncc1701.starfleet.fed>
"I'm a mechanic, not a doctor." Volker Borchert  <v_borchert@despammed.com>