Each Java class should have a @author tag in the class comments. When making (significant) changes, you should also add yourself in the list of authors. Always use your full name.
Javadocs and codes comments
Each Java class should have comments that clearly describe the purpose of the class. For interfaces specifically, each and every method must have clear comments.
Public methods should be commented if the meaning is not entirely clear from the method and parameters names (is it ever?). When the method overrides or implements a method, then repeating the javadoc is not needed.
Comments in the code are recommended when they explain a block of code or when they explain why things are done in a certain way. Repeating the code in human readable wording is wasteful.
General conventions
Use "@todo" comments to indicate shortcuts or hacks which should be fixed. Better still is just to do it right and not have the shortcut.
Import statements should never use wildcards. Always use the correct list of classes to import.
