Reflection / Java access

Very limited reflection is possible, but is not recommended. Use it in cases when KubeJS doesnt support something.

In 1.18.2+ internal Minecraft classes are remapped to MojMaps at runtime, so you don't have to use obfuscated names if accessing internal Minecraft fields and methods.

 

An example of adding a block with a custom material, built using reflection to get the MaterialJS class, then make a new instance of that with amethyst sounds and material properties from internal Minecraft classes.

// Startup script, 1.18.2
const MaterialJS = java("dev.latvian.mods.kubejs.block.MaterialJS")
const Material = java('net.minecraft.world.level.material.Material')
const SoundType = java('net.minecraft.world.level.block.SoundType')

amethystMaterial = new MaterialJS('amethyst', Material.AMETHYST, SoundType.AMETHYST) // f_164531_ and f_154654_ are the respective obfuscated names of these fields, for older versions

//This builder uses 1.18.2 syntax, it will not work in 1.16 or 1.18.1
onEvent('block.registry', event => {
	event.create('amethyst_slab', 'slab')
		.material(amethystMaterial)// Use the new MaterialJS instance we created as the material
		.tagBlock('minecraft:crystal_sound_blocks')
		.tagBlock('minecraft:mineable/pickaxe')
		.requiresTool(true)
		.texture('texture', 'minecraft:block/amethyst_block')
})

This does come at a cost, it takes 1-2 seconds to load this script, instead of the normal milliseconds. You should always import your classes at the top of the script, instead of in an event.