I have reached till here: https://imagej.net/ij/developer/source/index.html. But after that, I don't know where to download this ij package and how to implement it into my code. Just for context, I'm using java and eclipse for coding.
I have already added the jar package mentioned in this article in the sense that I can see this in my referenced libraries: Using Fiji image processing as a library in Java. But when I copy paste the code snippet given at the end it shows that the build path is not fully formed yet and I have to rebuild the path. Additionally, this article: https://albert.rierol.net/imagej_programming_tutorials.html#ImageJ uses a lot of ImagePlus to work with plugins-- something that is my future goal.