Is it bad to explicitly compare against boolean constants e.g. if (b == false) in Java?

Solution 1:

It's not necessarily bad, it's just superfluous. Also, the actual variable name weights a lot. I would prefer for example if (userIsAllowedToLogin) over if (b) or even worse if (flag).

As to the performance concern, the compiler optimizes it away at any way.

As to the authoritative sources, I can't find something explicitly in the Java Code Conventions as originally written by Sun, but at least Checkstyle has a SimplifyBooleanExpression module which would warn about that.

Solution 2:

You should not use the first style. I have seen people use:

• if ( b == true )
• if ( b == false )

I personally find it hard to read but it is passable. However, a big problem I have with that style is that it leads to the incredibly counter-intuitive examples you showed:

• if ( b != true )
• if ( b != false )

That takes more effort on the part of the reader to determine the authors intent. Personally, I find including an explicit comparison to true or false to be redundant and thus harder to read, but that's me.

Solution 3:

This is strongly a matter of taste.

Personally I've found that if (!a) { is a lot less readable (EDIT: to me) than if (a == false) { and hence more error prone when maintaining the code later, and I've converted to use the latter form.

Basically I dislike the choice of symbols for logic operations instead of words (C versus Pascal), because to me a = 10 and not b = 20 reads easier than a == 10 && !(b==20), but that is the way it is in Java.

Anybody who puts the "== false" approach down in favour of "!" clearly never had stared at code for too long and missed that exclamation mark. Yes you can get code-blind.

Solution 4:

The overriding reason why you shouldn't use the first style is because both of these are valid:

if (b = false) //...

while (b = true) //...

That is, if you accidentally leave out one character, you create an assignment instead of a comparison. An assignment expression evaluates to the value that was assigned, so the first statement above assigns the value false to b and evaluates to false. The second assigns true to b, so it always evaluates to true, no matter what you do with b inside the loop.