Saturday June 11, 2005

In my first favorite plugin entry I described Jalopy. The other external plugin I use is PMD.

PMD is a source code analysis tool which parses java source code, and then runs a large number of rules over the source code. For example, it checks for program errors, like double checked locking patterns, or overriding equals without overriding hashCode. It checks for potential program errors, like having an equals method with a single parameter that is not of type Object. And it checks for a number of coding style "violations", such as for example failing to use uppercase letters for class constants, or using excessively long or short variable names.

Here's a screenshot of PMD in action: you select a class or a package and run PMD on it, and all the rule violations are listed in the output window, where you can click to bring up the relevant source (or hit F12 and Shift F12 repeatedly to iterate forwards and backwards in the list.)

Thankfully, the ruleset is configurable. That's important, because I the default set of rules you get is not particularly good. It includes a rule I truly hate (and because I disagree with the result, I violate it all over my code, with the result that unless I customize the ruleset I get a bajillion rule violations when I run PMD on my code. I might write a rant about that rule in another blog entry...)

Customizing the ruleset is easy, once you know where to find the dialog: Tools | Options | IDE Configuration | Server and External Tool Settings | PMD Settings. Open the Rules customizer in the property sheet, and you get the following dialog:

Here you can move available rules to and from your chosen set of rules. Try adding all at first, then removing rules that get flagged in your code that you don't care about, or that you disagree with. More importantly, you can click on each rule to see a description and example of the kind of code that triggers the violation. This is really useful if you want to see if this is a rule you want to check for - and to get the rationale from the person who contributed the rule.

Note that you cannot get it to be happy if you use all the rules, since there are contradictory rules. For example, if your bean class has no constructor, you get the AtLeastOneConstructor violation telling you your class needs at least one constructor. But once you add one, the UnnecessaryConstructor rule will tell you that a constructor is not necessary when it's public and has no arguments! So learning how to configure the ruleset is essential.

I've been following PMD for quite a while. A couple of years ago I wrote a plugin that took the PMD integration a bit further in the IDE. I had written a suggestions window for NetBeans, and I plugged PMD into it, along with automatic fixers for some of the rules. So for example, if PMD flagged a method as unused, you could just double click to get a removal preview dialog, and then click again to nuke the method. Here's a screenshot of this in action on an unused field:

As you can see, this screenshot is old - look at the old icon style, or the old property sheet, and the old window manager... I think this was in NetBeans 3.4. (More suggestions window screenshots here)

Unfortunately, this was a hobby project, and I suddenly got extremely busy working on Creator since we were trying to design and develop it with a suicidal schedule, so my spare time become occupied by work instead. I haven't been able to keep it up, and now it looks like it will take some work to bring it up to speed. However, in the meantime part of the suggestions framework has been incorporated into standard NetBeans (specifically the TODO scan portion of it), and I saw some comments on the dev@tasklist alias that Jan Jancura is going to do some work in this area so perhaps we can get this going again.

It also looks like the PMD plugin itself on SourceForge is getting some attention with some recent development, so I think this going to get even better soon.

To download the plug-in, visit this link, download the most recent release, unzip it, and then from the Tools | Update Center choose to install a locally downloaded nbm file.