Navigating between occurrences
Eclipse can highlight occurrences of the selected variable / field / method, making it a lot easier to read existing code:

You can configure this under Preferences > Java > Editor > Mark Occurrences and change the highlighting style under General > Editors > Text Editors > Annotations. I like to enable the annotations in the vertical ruler, because they are easier to spot.
If you want to jump from one occurrence to the next one, you can choose Occurrences in the navigation toolbar and navigate using Ctrl + . and Shift + Ctrl + .

A bit more convenient is Search > Occurrence in File (Ctrl + Shift + U) which shows all occurrences in a separate view:
