New to Java

There is this open source project I use and modify for my personal, private use...

I would like some best-practice/practical experience suggestions on methodology/tools to maintain a growing number of source code patches I have created for said software. (FYI It is generally not mandatory that I upgrade to new version of the software when it comes out. Sometimes I will use the version I have for several versions before getting the new one, and re-implementing my changes. And sometimes I don't even implement the changes; I just run it vanilla.)

Currently, I download the latest code from SVN, make my changes to the original code files, and keep track of my changes in a text file, which I then dutifully reference to re-create them when I feel like re-synching with the official version. What I would like to have instead is a separate base of code that contains just my modifications, and somehow include/import it as painlessly as possible whenever I get a new version of the official code from SVN.

What's the best way to go about it? That's why I'm here.

I realize these situations rarely, if ever, work out perfectly, and I can deal with that. I just want to improve on how things are, now, in anticipation of where I can see them going!

I have some ideas about how to implement this, but they are of the "naive" variety and I think any tips I could get on method or tools to use would go far. I mean ... is it as simple as declaring new versions of affected methods in my patch code and marking them "overrides"? Also, probably a dumb question but will SVN that will help me do this?

Thanks for reading, and any response.

PS - Sorry if this is the wrong forum, but I am just looking for general, tip-of-the-iceberg type tips/links, so I figured folks could drop a quick answer here. TY!