I often hear from developers that with ABAP in Eclipse it is a little bit cumbersome to change the signature of a method while implementing the method body. For sure you can navigate very easily via the outline to the method definition part and add a parameter there and navigate back. But there is also the possibility to edit signature and body at the same time in eclipse.
Here you see a screenshot with two editors displaying the same source positioned in parallel editor windows:
The editor on top displays the signature and the editor below displays the body of the method.
Eclipse allows you to edit the code in both editors in parallel without getting into trouble concerning locking errors.
You can achieve this via the top level menu Window->New Editor. A new editor with the same source is opened and can be positioned in eclipse as you like.
Try it out.