diff : Java Glossary

A diff is a utility that shows you the differences between two files. Most of them overwhelm you with insignificant changes, such as an extra space after an open parentheses. An ideal diff would be aware of the language and:

• Deal with different line-ending conventions by telling you the files differ in line ending conventions, but not on every line. If the line ending conventions are inconsistent within either file, it should warn you of that.
• Tell you if either file has any trailing blank lines, but otherwise ignore them.
• Ignore space/spaces except where they are syntactically significant, unless you ask to see those differences too.
• Treat tabs as if they had been expanded to spaces.
• You should be able to tell it if comments are significant and/or the code is significant.
• When there are differences, see if they can be explained away by blocks being rearranged. This might be implemented by using a HashMap or digested HashMap to see if the differing line exists anywhere else in the other file, then looking before and after that line for a matching rearranged chunk.
• It might also work, in comparing two Java programs, to first tidy them both to canonical form, so the spacing is the same, keyword order is the same etc.

Tortoise Subversion has a primitive diff for comparing revisions in the source code repository.

DiffZilla

I mainly use DiffZilla, part of an old Visual Slick Edit version 6. It lets you notice the differences and copy lines between the files to make them more alike, or manually edit either file as you diff. It is not clever about spaces or rearranging. It is clever about differing line-ending conventions, however.