How to properly handle if statements containing both null checks and non-null checks together in an OR expression

Question

I have some code that does the following:

if(object == null || object.value.equals(" ")) {
    // do something
}
else {
   // do something else 
}

The above seems dangerous to me because if I switched the order of the two conditions or changed this to an AND expression, the code will crash when object is null, but I also read somewhere that Java guarantees operands are evaluated from left to right. That said, I also read do not assume this to be true.

I am confused by all this conflicting advice and wondering whether the above code constitutes a bug. That said, what is the best way to recode this if indeed this is considered bad practice?

Joop Eggen · Accepted Answer · 2023-01-10T05:36:49.787

2

In Java && and || are short circuit (boolean!) operators. So everything works as assumed. No unnecessary evaluation running into an error. Some languages Name these and-then, or-else.

boolean newGraphRequired = graphNode == null
    || gaphNode.timeStamp() != moduleNode.timeStamp();

Conditions become more straightforward.

edited Jan 10 '23 at 05:36

answered Jan 10 '23 at 05:13

Joop Eggen

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that's exactly the same as if I placed it in the if statement. If this is considered the elegant approach, that's what I prefer :) – Lauren_G Jan 10 '23 at 05:22
Yes and that is why I added my answer: other answers take a step too far. – Joop Eggen Jan 10 '23 at 05:25
1

I will edit my code kind sir ... thank you – Lauren_G Jan 10 '23 at 05:26
3

Not "shortcut", but [*short circuit*](https://stackoverflow.com/a/8759917/256196). – Bohemian Jan 10 '23 at 05:32
@Bohemian, thanks for the correction. Imagine propagating prologisms. – Joop Eggen Jan 10 '23 at 05:40
2

@Lauren_G don’t edit your question to become an answer. It’s confusing readers to have a “question” that says the same as the answer. – Holger Jan 10 '23 at 09:16

score 0 · Answer 2 · answered Jan 10 '23 at 04:48

0

Use below piece of code -

  if(object == null || (object != null && " ".equals(object.value))) {
        // do something
    }
    else {
        // do something else 
    }

Also Always keep constant values in left side of equals, it will prevent NPE.

For Above code if object is null or object.value is " "(space), it will go inside if otherwise it will go in else.

answered Jan 10 '23 at 04:48

what if the value is not a constant? – Lauren_G Jan 10 '23 at 04:51
If value is not constant then you will have to add one more null check as - object != null && null != object.value && object.value.equals("other non constant value"). Also I am not talking about object.value to be constant, its the other one like space in your case. – Jan 10 '23 at 05:04
@Lauren_G The reason to do `" ".equals(object.value)` is because `" "` is a "constant", and is guaranteed to not be `null`. The `String#equals(Object)` method will return `false` if the argument is `null` (it won't throw an NPE). – Slaw Jan 10 '23 at 05:10
1

The `object != null` test is obsolete at this place. It can’t be `null` at this point. – Holger Jan 10 '23 at 09:08

How to properly handle if statements containing both null checks and non-null checks together in an OR expression

2 Answers2