Is using the order of evaluation to check for null values bad practice?

Question

If I wish to perform two checks on a string, that it is not null, and that it is not 0 length, I could do this-

if(string != null) {
    if(string.length() > 0) {
        //Do something
    }
}

Or I could do this

if(string != null && string.length() > 0) {
    //Do something
}

As the first check is executed first, the second comparison doesn't happen and a NullPointerException isn't thrown.

Is the second method guaranteed to work in all cases? And if so, would it be considered bad practice to use it?

Order of operations is well defined in Java, so that's perfectly safe. It's also a pretty common way to do it. — resueman, Aug 25 '16 at 17:24
Using the `&&`, if the first check fails, the second is not evaluated. Also known as short-circuting. So it will not produce a `NullPointerException` — Orin, Aug 25 '16 at 17:24
Ok, thanks. That is what I assumed, however I didn't know if was guaranteed to always happen. — Theo Pearson-Bray, Aug 25 '16 at 17:26
[Java, check whether a string is not null and not empty?](http://stackoverflow.com/q/3598770) — Tom, Aug 25 '16 at 17:28

score 5 · Accepted Answer · answered Aug 25 '16 at 17:24

5

No, it is perfectly fine and guaranteed to work in all cases.

Reference from Java specification: https://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.7

answered Aug 25 '16 at 17:24

uoyilmaz

3,035
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25

score 1 · Answer 2 · answered Aug 25 '16 at 17:26

The one worth mentioning here: as you write such checks very often, it is advisable to put them into some dedicated helper method; such as:

static boolean doesStringContentContent(String value) {

or something alike.

And from an "improved" readability perspective, you might prefer coding that like

if (value == null) return false;
if (value.isEmpty()) return false;
return true;

But that doesn't matter too much - the important part is that you should not start copying around this check.

And finally, the one other possibility would to not return a boolean, but to have a

void checkStringHasContent(String value) {

which could throw a NullPointerException resp. some other thingy for an empty string.

score 0 · Answer 3 · answered Aug 25 '16 at 17:27

you are using && (and) operator in second expression. and nested if condition in first expression. in both cases you will get same result. because &&(and) operator execute second condition if only if first condition is true.

basically you are doing same thing in different manner.

Is using the order of evaluation to check for null values bad practice?

3 Answers3