It is often the case that something that needs equals() will also be displayed, even to the console, and that toString() needs to be better than the default Object.toString().
This check enforces toString() to be defined if equals() is defined.
It is based from the EqualsHashCodeCheck.
I have provided a patch from CheckStyle 4.3 and included unit tests and updates to messages.properties.
I've also tried to update the other languages but I can't guarantee that copy-and-paste is doing what I expect it to in UTF-8 format.