Coding standard for null checking [duplicate]

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Closed 14 years ago.

Possible Duplicates:
What's the comparison difference?
Null check in Java

Most of the developers have the habit of writing the null checking with null in the left hand side.like,

if(null == someVariable)

Does this help any way? According to me this is affecting the readability of the code.

• aioobe: Possible duplicate: stackoverflow.com/questions/3021195/…
• Aurelien Ribon: It's called "Yoda conditions" ! :D
• st0le: You mean, "Yoda Conditions, its called."
• user207421: 'Most of the developers'. Really? Evidence?
• T.J. Crowder: @EJP: Yeah, I don't see it very often at all. Perhaps it's most of the developers in his organization.

Answer 1

No, it has no purpose whatsoever in Java.

In C and some of its related languages, it was sometimes used to avoid making this mistake:

if (someVariable = null)

Note the = rather than ==, the author has inadvertently assigned null to someVariable rather than checking for null. But that will result in a compiler error in Java.

Even in C, any modern compiler will have an option to treat the if (someVariable = null) as a warning (or even an error).

Stylistically, I agree with you — I wouldn't say "if 21 you are, I will serve you a drink" (unless I'd already had (削除) a couple (削除ここまで) several and was doing my Yoda impersonation). Mind you, that's English; for all I know it would make perfect sense in other languages, in which case it would be perfectly reasonable style for speakers of those languages.

• st0le: @TJCrowder, to say it has no purpose whatsoever in java would be slightly wrong....If the someVariable is a Boolean, it doesn't throw a compile error...:) You'll need to Yoda that out...but otherwise java cleans up for you. :)
• T.J. Crowder: @st0le: Wow, I'm astonished to find that you're right about that. I did not know that (and have checked it). Thank you! But I'd counter with: Don't test booleans that way, there's no purpose whatsoever to if (someVariable == true), simply use if (someVariable) (and of course the !someVariable instead of comparing to false). (And the fact you can have an inadvertent assignment supports using that style.) The only time I'd use = or != with booleans would be if I were comparing two variables (not comparing to a constant), and the construct wouldn't help me there. :-)
• st0le: @TJCrowder, well ofcourse, no decent java programmer will actually use that...I was merely throwing an exception, pun intended ;)
• T.J. Crowder: @st0le: Yeah, thanks again. I was so surprised when I wrote a test case for it and it passed. :-)

Answer 2

It used to help in 'the olden days' when C compilers would not complain about missing an =, when wanting ==:

// OOps forgot an equals, and got assignment
if (someVariable = null) 
{
}

Any modern C#/Java/C++/C compiler should raise a warning (and hopefully an error).

Personally, I find

if (someVariable == null) 
{
}

more readable than starting with the null.

• mlvljr: (Speaking of C and C++ compilers): an error, not a warning?

Answer 3

In your case, I don't see any merit in doing that way. But I prefer the following...

if("a string".equals(strVariable))
{
}

over this..

if(strVariable != null && strVariable.equals("a string"))
{
}

• Cowan: @T.J. Crowder - yes, it is defined in the contract. From the very link you provided: "For any non-null reference value x, x.equals(null) should return false."
• Rosdi Kasim: @T.J. Crowder & @Cowan, yes I went back as far as JDK 1.1.1 and it is defined in the contract. tns.lcs.mit.edu/manuals/java-1.1.1/api/…
• T.J. Crowder: @Cowan & @Rosdi: I can't believe I've missed that all these years. Thanks. I've removed the earlier comment. Proof that you never stop learning. Man do those docs need rewording, all of the unnecessary reiteration of "for any non-null x" totally obscures the remaining points. And sadly, I've met quite a number of contract-breaking implementations of equals over the years. :-(