Is there any reason to use null == value condition in java?

Question

I am seeing this a lot in someone's code: null-check conditions are written like this:

if (null == value)

rather than

if (value == null)

I don't think there is any reason to have the null precede the operator in Java. Is there any benefit to doing it this way? Is this simply a case of a C++ programmer applying his skill to Java incorrectly, or am I missing something important?

do you have example code? i dont really understand the question... sorry — melli-182, Dec 05 '12 at 17:17
@MatiasCaamaño `if (null == value)` rather than `if (value == null)` — FThompson, Dec 05 '12 at 17:19
This sounds like a duplicate of http://stackoverflow.com/questions/3021195/which-is-more-effective-if-null-variable-or-if-variable-null — NPE, Dec 05 '12 at 17:19
Just a note for SO, please re-ask the question in the body of the post, and not just as the title. — Matt Clark, Dec 05 '12 at 17:19
People we do need 8 answers answering the wrong thing. The reason is to make sure we we do not write `value = null` instead of `value == null` since `null = value` would catch the error. — jn1kk, Dec 05 '12 at 17:24
@skynorth - in fact, it isn't the case at all. I'm aware of the difference (hence the mention of c++ programming in the original question) — bharal, Dec 06 '12 at 13:24

score 11 · Accepted Answer · edited Dec 06 '12 at 15:13

This is a case of so-called "Yoda Conditions" (item #1). Although it is possible to rationalize them in C/C++, there is no reason to use them in Java.

In C/C++, expressions of any type can go into ifs and whiles. Writing

if (var = NULL) // No compile-time error in C/C++

instead of

if (var == NULL)

is a common error among novices. Yoda conditions were supposedly a remedy to address this problem, at the cost of "Yodifying" your code: C/C++ would trap assignments to NULL

if (NULL = var) // Compile-time error

but "reversed" NULL checks are OK:

if (NULL == var)

Since Java considers non-boolean expressions inside control blocks of if, while, and for to be errors, it would trap var = null in place of var == null, triggering an error. Therefore, there is no reason to give up readability by "Yodifying" your expressions.

score 2 · Answer 2 · answered Dec 05 '12 at 17:20

Lets say you only want to print the contents of a String if it's longer than 20. You'll do this:

if (str != null && str.length() > 20) {
    System.out.println(str);
}

leaving out this str != null && would throw a NPE if str actually were null.

If you are referring to the difference of

if (str == null) { ... }

and

if (null == str) { ... }

there is none.

AlexWien · Answer 3 · 2012-12-05T19:19:02.373

1

The answer is NO!
There is absolutley not any need to prefer if (null == value) instead if (value == null) in java!

The check of if (null == value) , is a bit strange, at least in java, coming from code guidelines in C and C++, where that make sense.

I like more if (value == null) which is better readable.

The reason is to avoid the C/C++ error if (value = null) instead of correct if (value == null)

If you use if (null = value) the C/C++ compiler will throw an error.

However in java, even if (value = null) would be a syntax error.
So dont use that (null == value) in java

edited Dec 05 '12 at 19:19

answered Dec 05 '12 at 17:21

AlexWien

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i don't think this is true... in an `if` block you'd have a compiler error for value = null -- that is, if (value = null) won't compile – bharal Dec 05 '12 at 17:24

score 1 · Answer 4 · answered Dec 05 '12 at 17:25

1

It may read better some times

if( null == someFunction(someParameter, anotherParameter) )

vs

if( someFunction(someParameter, anotherParameter) == null )

answered Dec 05 '12 at 17:25

irreputable

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score 0 · Answer 5 · answered Dec 05 '12 at 17:19

0

It's typically an artifact of the developer's native language. Some languages have rules make null == value more natural than value == null. Syntactically, they are the same to Java.

answered Dec 05 '12 at 17:19

Mike Thomsen

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No, it is not the reason that there exitsts languages where "null == value" is more natural. It is simply a coding gudeline, to avoid accidently omitting one "=" instead of correct the "==" – AlexWien Dec 05 '12 at 17:32

rajah9 · Answer 6 · 2012-12-05T17:30:15.187

0

Not checking could mean a null pointer exception.

Placing it in this order helps you not confuse = (assignment) with == (equality).

both

if (a = null)

and

if (a == null)

will compile; however, you probably want the second and not the first.

If you flip them,

if (null = a)

will not compile, while

if (null == a)

will compile.

Thus you can catch a small, hard to find error at compiler time.

edited Dec 05 '12 at 17:30

answered Dec 05 '12 at 17:19

rajah9

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Indeed, but this doesn't answer the (interpreted) question about the difference between `null == value` and `value == null`. – FThompson Dec 05 '12 at 17:23
Edited my answer... Live long & prosper. – rajah9 Dec 05 '12 at 17:30
Decent answer now, but `if (a = null)` will not compile (unless `a` is a Boolean, but rarely are those set as null). – FThompson Dec 05 '12 at 18:10

score 0 · Answer 7 · answered Dec 05 '12 at 17:20

0

Just to make sure that you are not assigning a value for eg like value = null if you ommit == so this code will compile fine and it can be identified only during runtime, but if you try like this null = value this even won't compile.

answered Dec 05 '12 at 17:20

Pradeep Simha

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this isn't true... whatever if block i'm in will not compile with this – bharal Dec 05 '12 at 17:21
@bharal null = value will not even compile, it will throw compiler error – Pradeep Simha Dec 05 '12 at 17:27

Is there any reason to use null == value condition in java?

7 Answers7