Do I need to check null on both sides of an OR condition?

Question

Consider member variable:

String foo;

I only want to call setFoo if foo has not previously been set or currently is empty.

For this purpose, I am not sure if this is sufficient:

if(foo==null || foo.isEmpty()) {

  setFoo(foo);

}

Or is it safer to also check for null on the other side of the OR condition:

if(foo==null || (foo!=null && foo.isEmpty())) {

  setFoo(foo);

}

It wud have been easier, faster and more enlightening to have checked? :-) — Scorpion, Sep 04 '11 at 18:31

score 12 · Answer 1 · answered Sep 04 '11 at 18:28

12

if(foo==null || foo.isEmpty()) is sufficient.

In a Logical OR condition, Java will only evaluate the second part if the first part is false.

answered Sep 04 '11 at 18:28

jbx

21,365
18
90
144

2

In a *logical* OR expression. In *bitwise* OR, they are both evaluated. – Mark Peters Sep 04 '11 at 18:30
On a side note if u r going to have several such checks it is always a good idea to extract this into a method.. Something on the lines of StringUtils.. – Scorpion Sep 04 '11 at 18:32

score 4 · Answer 2 · answered Sep 04 '11 at 18:27

4

No, the first snippet is fine.

In Java (and in many similar languages like C or C++), the logical operators && and || perform short-circuit evaluation. In the case of ||, if the left-hand operand is true, then the right-hand operand won't be evaluated.

answered Sep 04 '11 at 18:27

Oliver Charlesworth

267,707
33
569
680

score 2 · Answer 3 · answered Sep 04 '11 at 18:39

2

Welcome to Stack Overflow

Operators like ||, && in Java are short-circuit operator, the second part of expression will only be checked when first part are not enough to determine the value

so, if(foo==null || foo.isEmpty()) is sufficient.

answered Sep 04 '11 at 18:39

Rangi Lin

9,303
6
45
71

score 0 · Answer 4 · answered Sep 04 '11 at 18:27

0

if (foo == null || foo.isEmpty()) setFoo(foo);

Works fine. In this case, if foo is null, setFoo(foo) will be called. If foo isn't null, and foo is empty, setFoo(foo) will also be called.

answered Sep 04 '11 at 18:27

fireshadow52

6,298
2
30
46

score 0 · Answer 5 · answered Sep 04 '11 at 18:41

0

I find it more elegant to use StringUtils.isBlank(foo) (from apache commons-lang), so you don't need the || at all.

answered Sep 04 '11 at 18:41

Arnout Engelen

6,709
1
25
36

But you have to have apache commons on the class path… – Alexey Ivanov Sep 04 '11 at 20:30
Yes, obviously. So put it there, learn how to use it and write beautiful code :). – Arnout Engelen Sep 04 '11 at 20:35

Do I need to check null on both sides of an OR condition?

5 Answers5