Overriden or Implemented?

When you override or implement a method, eclipse puts that annoying @Override annotation on it. I understand annotating methods that are actually overriding the superclass methods, but why on implemented methods?

Anyway, there is another way to differentiate between these methods. Eclipse puts an arrow (pointing up) in the sidebar next to every overridden/implemented method. Next to any overridden method, this arrow is filled in green, indicating a previous implementation by a super class. Implemented methods have a plain empty arrow.