Checkstyle

Checkstyle provides rules documented as standard checks in the section Javadoc Comments.

• JavadocPackage
• JavadocType
• JavadocMethod
• JavadocVariable
• JavadocStyle

PMD

PMD provides rudimentary support to check the existence of comments.

• UncommentedEmptyMethod
• UncommentedEmptyConstructor

Findbugs

Findbugs' concern is not on API documentation.