What's the comparison difference?

Question

Possible Duplicate:
Null check in Java

I'm just wondering what's the difference between

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

and

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

assuming that in both cases something is the same object. Presumably, there should be non, except for readability of the code.

Answer 1

The statements are completly equivalent.

Differences occure only when using equals, and then null is never used explicitely.

if( "A".equals(someString) ) { ... }

is null safe, since it doesn't fail if someString is null.

if( someString.equals("A") ) { ... }

will obviously fail when someString is null.

Answer 2

Check out this StackOverflow question: http://stackoverflow.com/questions/2369226/null-check-in-java. It covers the answer of your question.

Answer 3

There is no difference.

This is just to guard against the common mistake of using = in place of ==.

if (true = something) {...}

gives an error but

if (something = true) {...}

does not, assuming something is a boolean variable.

Answer 4

There is no difference.

The idea of putting the constant first helps guard against accidental assignment in the condition. For example in some languages it is valid to say:

if (i = 42) {
    ...
}

i is assigned and the condition is true. If you didn't mean to do this, there is no compiler error and it can be difficult to find.

If you instead always use:

if (42 == i) {
    ...
}

Then the day you accidentally do:

if (42 = i) {
    ...
}

A compiler error will alert you immediately that you are attempting to assign to a constant.

Answer 5

I also had a similar problem here is what I got as answers