Coding standard for null checking [duplicate]

Question

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.

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 a couple 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.

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.

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"))
{
}