Difference between null!=variable and variable!=null

Question

What is the difference between null!=variable and variable!=null Which method is perfect to use?

if ((null != value1) || (null != value2) || (null != value3)) {
            .......
            .......
            .......
}

or

if ((value1 != null) || (value2 != null) || (value3 != null)) {
                .......
                .......
                .......
}

Please suggest the best one and the logical change between these?

No difference. In the olden days, well perhaps still today ;-), constant != x was often recommended in languages like C. This was called Yoda Conditions and helped to avoid cases like x = constant as constant = x would raise a compiler error. (However, in Java the only case when this matters is when doing a comparison with a boolean which should be avoided anyway.) — user2864740
– user2864740, Commented Sep 17, 2014 at 5:03
I have seen codes comparing null with variable, that's why I asked this question. — JiniKJohny
– JiniKJohny, Commented Sep 17, 2014 at 5:06
Well, you have to make sure the expression is not null before a method is attempted to be invoked upon it - lest a NPE is raised. However it doesn't matter if it is null != x or x != null. Pick one and be consistent (which also means following the form already used in a project). — user2864740
– user2864740, Commented Sep 17, 2014 at 5:06

Peter Pei Guo · Accepted Answer · 2014-09-17 05:05:56Z

6

No difference.

But people quite often write "abc".equals(foo), instead of foo.equals("abc"), to avoid null point exception.

answered Sep 17, 2014 at 5:05

Peter Pei Guo

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Comments

Thihara · Accepted Answer · 2014-09-17 05:09:36Z

4

Nothing is different.

I prefer value != null for purely readability reasons.

edited Sep 17, 2014 at 5:09

answered Sep 17, 2014 at 5:03

Thihara

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Ananth · Accepted Answer · 2014-09-17 05:27:16Z

3

Both the ways of comparision are correct.There is logically no difference but programmers prefer to use value!=null.

answered Sep 17, 2014 at 5:27

Ananth

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Owen Cao · Accepted Answer · 2014-09-17 05:17:15Z

2

null != value is a hold-over from C. In C, your code will be compiled with no warning in this way: if (variable = null) (it's a wrong code), while you actually probably meant if (variable == null).

But in Jave both these two styles are OK.

answered Sep 17, 2014 at 5:17

Owen Cao

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bbaassssiiee · Accepted Answer · 2014-09-17 22:37:05Z

2

In C assignment looks similar to comparison:

lvalue = rvalue;
lvalue == rvalue;

lvalues (variables) can be assigned to. rvalues can be expressions. Null cannot be assigned to, so if you adhere to use null as the lvalue in comparison, then the compiler will catch the ommision of the second equal sign in a statement like

null = rvalue;

Where you might accidentally assign null with:

lvalue = null;

answered Sep 17, 2014 at 22:37

bbaassssiiee

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Alex Gwartney · Accepted Answer · 2014-09-17 05:12:06Z

1

As others have mentioned there is not a difference but I haven't ran across something that is

null != value2

I always see it as value2 !=null and like thihara said its easier for readability. I think its also good to keep it the way value != null for beginner programmers who could possibly go over some ones code might get a little lost on the concept even though there is no difference.

answered Sep 17, 2014 at 5:12

Alex Gwartney

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