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How to avoid “!= null” statements in Java?
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- 4Dupe: stackoverflow.com/questions/271526/…Justin Ardini– Justin Ardini2010-07-29 14:33:44 +00:00Commented Jul 29, 2010 at 14:33
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4 Answers
A first answer is to always return empty Lists, Sets, Arrays instead of null for method returning this kind of objects. Item 43 of Effective Java second edition from Joshua Bloch
4 Comments
Manuel Selva
@Mark Yep, I updated my answer while you where writing your comment ;-)
ToVine
Link is no longer active, just leads to the Java technetwork site
GC_
@ManuelSelva Broken Link
Manuel Selva
@GC_ Fixed, thank you.
Take a look at the Null Object Pattern. The basic idea is you have a special version of your class that you can use instead of null.
This special version has fields set to default values that make sense in your code. It means that you never have null references, you just have a class that doesn't do much or returns default values when used.
3 Comments
Carl Manaster
+1. Empty collections are almost a special case of this - you just don't need to write a class for them. But the pattern of handing around something that isn't null and behaves safely is the same.
Robin
Although good in some situations, I find it is fairly limited in real world usage.
Matt Warren
@Robin, yeah it has some limits, but it does beat getting NullReferenceExceptions!!
In my opinion, null checks are evil. They show that there is no contract that establishes whether obj may be null or not. The good alternative would be to write the code in such a way that obj is guaranteed never null. For example: if a getter must get a non-null obj, but cannot, it must throw an exception itself.
3 Comments
matt b
On the other hand, for many contracts,
null is an acceptable value. So you wouldn't want to eliminate ever checking for null, only eliminate the defensive need to check everything.
Vlad
@matt: indeed. however the check for null can be done not before using the object, but immediately after getting it.
Oliver Watkins
exactly. If null checks are everywhere in the code, it shows that the code is poorly written.
if (CONST_VALUE.equals(obj)) { ... } 5 Comments
Brian Knoblauch
While very effective, that does impair readability some.
Yuval Adam
Totally agree, readability is severely impaired. But this is an idiom which you should be familiar with, and not afraid to use on occasion.
Oliver Watkins
it also hides potential null pointer exceptions which can be bad
ToVine
@OliverWatkins why? By using the equals(Object) method of the CONST_VALUE object, it will never throw a NPE (assuming that the CONST_VALUE is a, well, constant that's already been initialized)
Oliver Watkins
yes it they are constants it should be fine. But it reads badly : obj.equals(CONST) reads far better than CONST.equals(obj)