If you use Eclipse you can open the workspace found in \mcp9xx\eclipse. You will have to correct the library path for the vanilla jar and realms jar, and also add libraries for JRift, json, asm, and ...

If you want to build a music mod in Arma 3 for mission triggers or to use whilst zeusing, you may be discouraged by the painfully long time it takes to create the file hierarchy and various code files ...