Java syntax: (condition ? something : something) what does it do?

[Claryn]

Hi. 

I have come across some notation in Java that I don't understand what means:

 

	Obj o1, o2 = null;
    	(...)
        o1 = (o2 != null ? o2 : o1);

        

What does that last line do? 

To me, it looks like the form is: (condition ? something : something)

[mariushm]

if condition then something else something

 

It's used in a lot of languages, it's called ternary operator : https://en.wikipedia.org/wiki/%3F:

 

[Nuluvius]

It's a Ternary Operator.

[yusufZD]

It is called ternary form. Short hand notation of if-else.

[Claryn]

Aah soo:

String true = True ? "True" : "False";
String false = False ? "True" : "False";

[mariushm]

If you want to really confuse someone then yes.

 

function isReallyFalse ($value) {

return ($value===FALSE) ? TRUE : FALSE;

}

would probably be a better example (in PHP above).

 

[Dat Guy]

Actually, that would be a horrible example because it is an unnecessarily verbose wording for "return !$value".

[Claryn]

3 minutes ago, mariushm said:

If you want to really confuse someone then yes.

 

function isFalse ($value) {

return ($value==FALSE) ? TRUE : FALSE;

}

would probably be a better example (in PHP above).

 

I don't know PHP, but I could make it less confusing:

 

result = a > b ? a : b;

does this:

if (a > b)
	result = a;
else
	result = b;

Am I correct?

[Dat Guy]

Yes, you are.

[mariushm]

Just now, Dat Guy said:

Actually, that would be a horrible example because it is an unnecessarily verbose wording for "return !$value".

Well, yes and no. It was a bad example. I modified the example to be more correct.

 

In PHP you don't have to specify data type for each variable, so some variables are converted to boolean by some rules which you may or may not agree with. See http://php.net/manual/en/language.types.boolean.php#language.types.boolean.casting

I've changed the example code to do strict checking and be more correct. Using  !$variable would just do a plain == comparison internally, so an empty array for example could return FALSE which you may not want.

 

 

[Dat Guy]

It's still a bad example:

 

function isReallyFalse ($value) {
	// Horrible version:
	// return ($value===FALSE) ? TRUE : FALSE;
	// Amazing version:
	return $value===FALSE;
}