Side-by-side diff viewer, editor and merge preparer
tkdiff is a graphical front end to the diff program. It provides a side-by-side view of the differences between two text files, along with several innovative features such as diff bookmarks, a graphical map of differences for quick navigation, and a facility for slicing diff regions to achieve exactly the merge output desired.
Launch an external diff tool like WinMerge in Eclipse
...Furthermore the plugin can (optional) format java code before the compare. This simplifies the compare if the code of 2 versions of a file is different formatted.