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From "Nathaniel Alfred" <Alfred.Nathan...@swx.com>
Subject RE: Coding style question: backwards null checks
Date Sat, 08 Mar 2003 14:29:09 GMT
> -----Original Message-----
> From: Berin Loritsch [mailto:bloritsch@apache.org]
> Sent: Freitag, 7. März 2003 18:50
> To: cocoon-dev@xml.apache.org; dev@avalon.apache.org
> Subject: Re: Coding style question: backwards null checks
> 

> > if ( "something".equals(stringToCompare) {
> >    ...
> > }
> > 
> > IMO it seems more straightforward and easier to read if it's:
> > 
> > if ( stringToCompare.equals("something") ) {
> >    ...
> > }
>
 
> Actually, this *does* have a purpose.  In the event that
> stringToCompare is null, then you would get spurious
> NullPointerExceptions that are not always easy to trace.
> 
> The "something".equals(somethingElse) guarantees that
> you won't get the NullPointerException every time without
> resorting to the longer form of:
> 
> if ( stringToCompare != null && 
> stringToCompare.equals("something") ) {
>      ....
> }
> 
> It's a lot more typing to be _truly_ functionally
> equivalent.  The compiler cannot guarantee that
> the stringToCompare variable is never null, so it
> will not give you a warning.

I'd say this is no longer a matter of taste but of methodology.  
If you write

  stringToCompare != null && stringToCompare.equals("something") 

you state clearly that you expect it may be null and how to deal
with it.  Saying that you write 

  "something".equals(stringToCompare)

because you *know* from long years of experience that it is 
equivalent, gains you an entry in the Java obfuscation contest.

(I am fairly seasoned Java programmer but I had to look up docs
to convince myself that equals(null) wouldn't throw an exception.)

A null string being different to any other string may be in some
cases a useful convention, in other cases it hides a logic error.

Let the code state clearly what your intentions are and let it fail
with NPE, if you don't expect handle nulls.

NB my stanza for repeatedly writing non-null checks is:

  if( stringToCompare == null )
      stringToCompare = "";
  if( stringToCompare.equals("something") ) {
      ...
  }

Cheers, Alfred.

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