Is it good practice to check for null and check object properties in the same if statement

Question

Is it good practice to check for null and check object properties in the same if statement?

Consider the following code:

if (jamesBlunt != null && jamesBlunt.isReallyBad()) {
   // Don't buy his records
}

This particular code is in java and I know the expression is evaluated from left to right so technically it won't throw a NullPointerException but in general is this good practice in any language?

Answer 1

I'll assume the || is a typo and you meant && :)

To answer your question: it depends.

Does it make sense for jamesBlunt to ever be null? If not, then it would be better practice to have something like this:

void buyARecord(Artist jamesBlunt) {
    if (jamesBlunt == null) {
        throw new IllegalArgumentException("James should never be null!");
    }
}

If it does make sense for jamesBlunt to be null then your approach is fine, assuming null and isReallyBad mean the same thing semantically. If they mean different things semantically then you should probably not be combining them on one line.

You do need to be careful in other languages. Many (Java, C++, C# etc) will behave the same way, but some may evaluate from right-to-left or evaluate lazily. Take particular care with functional languages like Lisp and Scheme as they tend to behave differently to object oriented languages like Java and C#.