Is there any difference between (null == var) and (var == null)

Question

I want to know differences between two conditional expressions null == var and var == null in if statement of Java.

`null==var` called [Yoda condition expression](http://en.wikipedia.org/wiki/Yoda_conditions). `var == null` can be misspelled as `var = null` code will run but if `null==var` will misspelled then it would be compilation time error. Read also [Criticism](http://en.wikipedia.org/wiki/Yoda_conditions#Criticism) — Grijesh Chauhan, Sep 23 '13 at 10:05
@GrijeshChauhan The most possible reason,You should write that as as anwer. — Suresh Atta, Sep 23 '13 at 10:09
@sᴜʀᴇsʜᴀᴛᴛᴀ lets add my comment in your answer. usually I rearly answer Java's questions. — Grijesh Chauhan, Sep 23 '13 at 10:12

Suresh Atta · Answer 1 · 2013-09-23T10:37:29.677

8

There is no difference.Simply a matter of style.

And the first one called as yoda style

In programming jargon, Yoda conditions (also called Yoda notation) is a programming style where the two parts of an expression are reversed in a conditional statement.

Although both conditional expressions null == var and var == null are equvilent. But suppose if you introduces bug by misspell == (check equality ) as = (assignment) then var = null doesn't give you can error and introduce a bug in your code. Whereas you write null == var and suppose misspells null = var it produce a compilation time error. And a compilation time error is a way better than a runtime error. That's one of the advantages of the Yoda conditional form.

But I also suggest you read Criticism of Yoda continuations:

Many Programmers hate it, as it has to mentally re-reverse it to understand it. (Others obviously don't have that issue). The practice is referred to as "Yoda conditions". Most compilers can be persuaded to warn about assignments in conditions anyway.

edited Sep 23 '13 at 10:37

answered Sep 23 '13 at 10:06

Suresh Atta

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For mentioning the Yoda condition, +1 you get. – André Stannek Sep 23 '13 at 10:08
Well.. correct..I think now it should be helpful for OP :) – Grijesh Chauhan Sep 23 '13 at 10:48
@suresh In Java: Is `if(var == NULL)` is same as `if(!var)` **?** – Grijesh Chauhan Sep 23 '13 at 14:24
@GrijeshChauhan Nope.To successfully compile the statement if(!var), here `var` must be a boolean type. Where as in condition if(var == null), `var` can be any object reference. – Suresh Atta Sep 23 '13 at 14:35
@sᴜʀᴇsʜᴀᴛᴛᴀ Oh we can do this in C/C++, so I wanted to suggest OP that right `if(!var)` instead of `null == var` and `var == null`. But not possible in Java. – Grijesh Chauhan Sep 23 '13 at 14:38
Yes.If OP do `if(!var)`,OP land up in a compiler error that states `The operator ! is undefined for the argument type(s) var`, If it a object reference,other than a `boolean`. – Suresh Atta Sep 23 '13 at 14:41

score 2 · Answer 2 · edited Dec 30 '13 at 12:54

2

There are no difference. for example consider the following piece of code

String x = null;
if(x==null)
{
    System.out.println("null");
}
if(null==x)
{
    System.out.println("no diff");
}

output

null
no diff

This means that there are no difference

edited Dec 30 '13 at 12:54

Grijesh Chauhan

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answered Sep 23 '13 at 10:06

SpringLearner

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score 2 · Answer 3 · edited May 23 '17 at 12:33

2

You can also have a look at this:

Which is more effective: if (null == variable) or if (variable == null)?

edited May 23 '17 at 12:33

Community

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answered Sep 23 '13 at 10:20

Sascha M

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Good link but better to mark duplicate then post it as answer. +1 as I think you don't have privilege to mark duplicate. – Grijesh Chauhan Sep 23 '13 at 10:33

score 0 · Answer 4 · answered Sep 23 '13 at 10:05

0

No, there's not. Both statements are true exactly when var is null.

answered Sep 23 '13 at 10:05

chrylis -cautiouslyoptimistic-

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Is there any difference between (null == var) and (var == null)

4 Answers4

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