Here's what it looks like:
|Screenshot from Redundancy Checker|
You can also change the settings, controlling for how close the words or phrases need to be, and what words should be skipped for being too common:
|The Options window|
Finally, you can edit the text and save it. So the program works, and does all the things I set out to do, but it doesn't necessarily do them well. The biggest issue is that the RTFEditorKit in Java is buggy. It doesn't read smartquotes properly, and it can lose other basic formatting too. So loading a file, editing it to fix the redundancies, and saving it isn't really an option. I'm not sure how, or even if, I can fix it. I suppose I could make my own RTF parser, but that would be quite a pain, and I don't really think it would be worth the time.
Update: One thing I've realized is that the source code for the RTFEditorKit is available. Rather than replacing it, I could edit the original. I'd have to check to see how the code was licensed. I should probably create a class that extends the kit, and then only modify the methods I need to.