Iterating over the content of a text file line by line - is there a best practice? (vs. PMD's AssignmentInOperand)

Question

We have a Java Application that has a few modules that know to read text files. They do it quite simply with a code like this:

BufferedReader br = new BufferedReader(new FileReader(file));  
String line = null;  
while ((line = br.readLine()) != null)  
{  
   ... // do stuff to file here  
} 

I ran PMD on my project and got the 'AssignmentInOperand' violation on the while (...) line.

Is there a simpler way of doing this loop other than the obvious:

String line = br.readLine();  
while (line != null)  
{  
   ... // do stuff to file here  
   line = br.readLine();  
} 

Is this considered a better practice? (although we "duplicate" the line = br.readLine() code?)

Answer 1

I generally prefer the former. I don't generally like side-effects within a comparison, but this particular example is an idiom which is so common and so handy that I don't object to it.

(In C# there's a nicer option: a method to return an IEnumerable<string> which you can iterate over with foreach; that isn't as nice in Java because there's no auto-dispose at the end of an enhanced for loop... and also because you can't throw IOException from the iterator, which means you can't just make one a drop-in replacement for the other.)

To put it another way: the duplicate line issue bothers me more than the assignment-within-operand issue. I'm used to taking in this pattern at a glance - with the duplicate line version I need to stop and check that everything's in the right place. That's probably habit as much as anything else, but I don't think it's a problem.