Should parenthesis always be placed around the ternary operator?

Question

Checkstyle complains about the following:

return (null == a ? a : new A());

and says the parens are unnecessary.

While the statement certainly works fine without them, it seems far more readable with them present---otherwise as I'm reading it I tend to see:

return null

first and then have to pause to consider the remaining

== a ? a : new A(); 

part, since my brain has already gone down one path.

Furthermore, I tend to do the same thing whenever I see a ternary operator, unless it is grouped in parens.

So: should parens around the ternary be the de facto standard? Is there ever any reason to not put them there?

Answer 1

When reading a return statement, I know that everything between 'return' and ';' is what is going to be returned, so there is no way I can read your code sample as return null followed by some symbols as you claim you read it.

Perhaps reading up on parsing techniques might help you to see it as I do. That said, I haven't really read up on parsing techniques, though I've cobbled a few parsers together over the years.

I always remove unnecessary parentheses. They don't aid in code comprehension, as I know Java's operator precedence pretty well. The odd time I'm unsure, I add parentheses and wait to see whether IDEA tells me they're redundant. Then I remove them, and try to commit to memory the precedence rule I've just discovered.

In the codebases I inherited, I tend to find the greatest number of redundant parentheses in areas of code that are poor for other reasons, so I associate the two.

Answer 2

In general, no.

Parentheses are not required around ternary (also known as conditional) operators or its sections, because their precedence is so very low in the order of operations (just below logical operators and above assignments). See the link below for the full table.

It could be argued, therefore, that such unnecessary parens visually clutter the code, and they reveal a lack of comprehension on the part of the programmer.

Exceptions that might require use of parens in or around ternaries would be:

• If your ternary is complex enough to merit multiple lines; you might then surround your statement in parens in order to prevent automatic semicolon insertion.

• If your ternary is nested within another ternary.

See also on MDN:

• Operator precedence (order of operations)

• Conditional (ternary) operator

• Automatic semicolon insertion