Did you know we're out of DocCheck doclet? There's no more way to get it. I'm appalled.
When you write Java code, you write inline documentation of your code, that's called Javadoc. It's been found so useful over years that people even went looking after missing Javadoc throughout their code. (If appropriate time was given to write it, it must have been documented correctly, and it will be maintainable in the future. That's the whole point.)
So, when you're documenting 1,000 classes that each have 10 methods and 10 variables to be documented, you might forget some. You might also forget to document parts of the methods, like the parameters.
...People went looking for missing Javadoc throughout their code and that's a daunting task. That's where the DocCheck doclet helps a lot. It's a doclet (you can think of it as a plugin for Javadoc) that produces documentation about the documentation. Especially, it provides the user with an analysis of missing Javadoc, poorly syntaxed Javadoc, and may even output all that as statistics. When you're doing development, that's a major quality tool.
And, yet as I said, we're out of DocCheck. DocCheck hasn't evolved since the mid-2000's. It's been put aside as more emphasis was put on freeing Java, producing Java 6 and, soon, Java 7. Now, it's obsolete.
If you still do want to download an old version, in order to try and adapt it to today's needs, you won't even find the right place to download it nor instructions to install it. Oracle bought Sun since then, and they broke a lot of download links. They've been told about that and they didn't react, so it seems DocCheck isn't in their priorities.
Besides, DocCheck's been put aside of the current Java 7 specifications. We might only see a new version for Java 8, possibly in five years...
There are others tools to do the same. The great advantage of DocCheck was that it integrated seamlessly into the ubiquitous Javadoc tool.