I occasionally see people ask “when I am learning modding, should I stick to Java or pick a different JVM language like Kotlin?” I understand why people want to avoid Java but I think you should stick to Java. Here are the reasons:
Minecraft is written in Java. Fabric and Neoforge are both written in Java.
So while it is possible to interact with Minecraft through a language like Kotlin or Scala, it is not nice. Minecraft and modloader APIs will not feel “idiomatic” in your preferred language; they will feel like Java code. It will be difficult to use your language’s unique, non-Java features to interact with things from Minecraft.
Maybe your exposure to Java is through Spring Boot, Jakarta, or heinous object-oriented projects in undergrad. Minecraft does not feel like that. They basically write Java like it’s C++; they don’t use reflection, serialization, annotations, or factory builder builder-factory builder beans. It’s not so bad.
Not only will you need to understand Kotlin, you will need to
understand how Kotlin maps
onto Java bytecode. You’ll need to get comfortable with @JvmStatic,
what a companion object actually is, etc.
You’ll also need to understand the reverse – how Java maps back onto Kotlin – because every time you look at a learning resource or look at code from the loader or game, you will be looking at Java. If you’re going to be thinking about Java in your head anyway, why not cut out the middleman and just write the Java you’re thinking about?
Most modders use Java.
If you are only familiar with Java 6 or something, you’re missing out
on lambda functions, records, pattern-matching instanceof,
pattern-matching switch, streams, new convenience
functions, and a whole host of other things. I personally think it is
very fun to write “modern Java”.
If this is starting to sound complicated: you don’t have to use these language features if you don’t want. You don’t need to know all of Java inside and out to write mods. But these features will be there for you when you want them.
Minecraft mods are able to directly change the code of Minecraft using a brilliant library called Mixin. Mixin is able to weave the JVM bytecode of your method into the JVM bytecode of a method from Minecraft. It’s exciting stuff, but it’s as hacky as it sounds, and everything needs to be set up just so in order for the weaving to work.
So you will need to write your mixins in Java. Even mods that use Kotlin end up with a separate Java source-set just for the mixins.
I’ve heard from several prospective modders that they’re considering non-Java languages to cut down on “boilerplate code”. To be frank, Minecraft modding does not involve that much “boilerplate code”.
(Instead, the boilerplate exists in the form of “a steaming pile of JSON files you need to write”, but that’s a story for another day.)
There are some old books on “modding minecraft with Python” and such. These all rely on someone’s library to do the heavy lifting for you. Every single one is out of date. Don’t bother.
I think these products are aimed at two audiences:
People who aren’t really interested in writing full-fat Minecraft mods, but they just want to learn programming inside a visual environment. If you want to draw some pictures and learn programming in the process, there are non-Minecraft ecosystems like Scratch and Processing that are better suited for learning, very visual, and much more well-supported with high-quality learning materials.
If you are just starting your computer programming journey, I don’t want to dissuade you from having fun with Minecraft, but I also don’t want to sic the ridiculous moving-target spaghetti-code Minecraft ecosystem on you either.
People who have learned Python in the past. But: if you have learned one programming language, picking up a second is so much easier. So I would not worry about “I know python but I don’t know java, so I can’t do modding”, because you will be up-to-speed on Java within a week.