Re: null testing

From:

Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 30 Jun 2009 07:56:22 -0700

Message-ID:

<qIp2m.14170$WC2.6567@newsfe10.iad>

Dirk Bruere at NeoPax wrote:

jnizet wrote:

On 30 juin, 16:32, Dirk Bruere at NeoPax <dirk.bru...@gmail.com>
wrote:

Two lines of code

if ( stationsStr==null || stationsStr.equals(""))

if (stationsStr.equals("") || stationsStr==null)

When stationsStr==null the second line throws exception, but the first
one does not. I assume that in the first line it sees the condition
satisfied and does not test for the second condition. Does this make the
code compiler dependent?

No. It's specified in the JLS. All compilers will ignore the second
test if the first one succeeds.
The same goes for && :
if (stationsStr != null && stationsStr.equals(""))
won't throw an NPE if stationsStr is null.

JB.

OK. However, I think I'll test separately anyway so the ordering is
apparent to anyone maintaining the code.

That is often a good idea, but "p != null && p.something" is a common
idiom in many c-descendant languages, so most maintainers will have no
problem with the ordering.

Note: "".equals(null) will *not* throw an NPE, so the order wouldn't
really be that important.

Also, the apache-commons-lang library has a great utils class called
StringUtils, which has very useful methods:
StringUtils.isEmpty(myString), and StringUtils.isBlank(myString) to name
only two. The JavaDocs for each StringUtils methods explain clearly what
the return values are for all the edge and common cases.

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>