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

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 · 2023-01-10 05:36:49Z

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, 2023 at 5:36

answered Jan 10, 2023 at 5:13

Joop Eggen

110k8 gold badges89 silver badges142 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Lauren_G Over a year ago

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 :)

Joop Eggen Over a year ago

Yes and that is why I added my answer: other answers take a step too far.

Lauren_G Over a year ago

I will edit my code kind sir ... thank you

Bohemian Over a year ago

Not "shortcut", but short circuit.

Holger Over a year ago

@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.

|

user19443549 · Accepted Answer · 2023-01-10 04:48:14Z

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, 2023 at 4:48

user19443549

4 Comments

Lauren_G Over a year ago

what if the value is not a constant?

user19443549 Over a year ago

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.

Slaw Over a year ago

@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).

Holger Over a year ago

The object != null test is obsolete at this place. It can’t be null at this point.

Collectives™ on Stack Overflow

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

2 Answers 2

6 Comments

4 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

4 Comments

Linked

Related