Since Oracle has taken over Sun websites, a number of links are broken, among which the download link in the following page
(although this page is an Oracle one it still points to a no longer existent Sun site)
Does anyone know where to find the doccheck.jar utility ?
Even if a valid download link would still exist (I can't find any), likely the thing doesn't help you as it hasn't been updated for Java 5+. You would only be able to use it on really old javadocs generated with JDK 1.4 and below.
Funny enough, the only working download link I could find is this: