Checkstyle rule to avoid not condition

Question

I am using checkstyles and I'd like to define the rule like where it displays a warning in case someone uses not condition under if ... else ... block. For example:

if (!employeeNotExist) { 
  // code
} else {
  // code
}

Reason being it's good to have only positive condition for readability

Is there ready made module for this under checkstyle or some custom checkstyle rule needs to be written for this?

Norbert Radyk · Accepted Answer · 2014-05-15 07:09:12Z

1

I don't think this check is defined in checkstyle itself, but you can always use one of the extension plugins i.e. https://github.com/sevntu-checkstyle/sevntu.checkstyle, where you can find what you're after here: here.

answered May 15, 2014 at 7:09

Norbert Radyk

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1 Comment

user3198603 Over a year ago

i am using eclipse-cs plugin

barfuin · Accepted Answer · 2014-05-19 14:50:12Z

1

Checkstyle cannot do this out of the box. So if using a third-party library is no option for you, you will have to write a custom check. If it's any comfort: This would be quite a simple case of custom check.

The best you can do out of the box is to configure a DescendantToken check like this (works in Eclipse-CS; DescendantToken checks are complex low-level checks which require understanding of the AST to configure, please see the linked documentation for more information):

<module name="DescendantToken">
    <property name="tokens" value="LITERAL_IF"/>
    <property name="limitedTokens" value="LNOT"/>
    <property name="minimumDepth" value="2"/>
    <property name="maximumDepth" value="2"/>
    <property name="maximumNumber" value="0"/>
    <property name="maximumMessage" value="Consider changing this to a
            positive condition for better readability."/>
</module>

This approach is somewhat crude, as it will not detect if there is an else block, and it also flags method calls such as if (!map.isEmpty()). But it covers your if (!employeeNotExist) case. It will also flag conditions like !(a || b), but those can be rewritten to !a && !b.

So, all in all, it's far from perfect, but this is the closest you're going to get with out-of-the-box Checkstyle.

edited May 19, 2014 at 14:50

answered May 16, 2014 at 13:53

barfuin

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5 Comments

user3198603 Over a year ago

Thanks Thomas. What do you mean by false positives ?

barfuin Over a year ago

False positives are cases where the check reports an issue, but in reality everything is good. In contrast, a false negative is a case where the check misses an issue.

user3198603 Over a year ago

As i stated in OP, i want to flag only if else blocks where if contains not operator( i dont want to flag where if without else contains not operator)

user3198603 Over a year ago

Also i did not get what minimumDepth, maximumDepth, minimumNumber, maximumNumber means ? It would be helpful if you explain the term giving some example. Thanks in advance.

barfuin Over a year ago

Right, this won't consider any else blocks. I updated the answer to clarify. My answer shows what's possible without a custom check. I am aware that it's not your desired solution, but it is all you can do without writing your own check. This may still help to provide a basis for a manual inspection run.

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