code

package com.steelfeathers.nethersurvival.worldgen;

import java.util.Random;

import com.steelfeathers.nethersurvival.blocks.BlockCrystalCluster;
import com.steelfeathers.nethersurvival.init.ModBlocks;
import com.steelfeathers.nethersurvival.worldgen.predicates.NetherGenPredicate;
import com.steelfeathers.nethersurvival.worldgen.predicates.OverworldGenPredicate;

import net.minecraft.init.Blocks;
import net.minecraft.util.math.BlockPos;
import net.minecraft.world.World;
import net.minecraft.world.chunk.IChunkGenerator;
import net.minecraft.world.chunk.IChunkProvider;
import net.minecraft.world.gen.feature.WorldGenMinable;
import net.minecraft.world.gen.feature.WorldGenerator;
import net.minecraftforge.fml.common.IWorldGenerator;

public class CrystalGenerator implements IWorldGenerator {

    private WorldGenerator crystal_nether;
    private WorldGenerator crystal_overworld;

    public CrystalGenerator() {
        crystal_nether = new WorldGenCrystal(ModBlocks.crystalCluster.getDefaultState(), Blocks.NETHERRACK, 5, 3, BlockCrystalCluster.FACING);
        crystal_overworld = new WorldGenCrystal(ModBlocks.crystalCluster.getDefaultState(), Blocks.STONE, 5, 3, BlockCrystalCluster.FACING);
    }

    @Override
    public void generate(Random random, int chunkX, int chunkZ, World world, IChunkGenerator chunkGenerator,
            IChunkProvider chunkProvider) {
        switch (world.provider.getDimension()) {
        case 0: //overworld
            this.runGenerator(crystal_overworld, world, random, chunkX, chunkZ, 10, 0, 64);
            break;
        case -1:  //nether
            this.runGenerator(crystal_nether, world, random, chunkX, chunkZ, 30, 0, 64);
            break;
        }

    }


    private void runGenerator(WorldGenerator generator, World world, Random rand, int chunk_X, int chunk_Z,
            int chancesToSpawn, int minHeight, int maxHeight) {
        if (minHeight < 0 || maxHeight > 256 || minHeight > maxHeight)
            throw new IllegalArgumentException("Illegal Height Arguments for WorldGenerator");

        int heightDiff = maxHeight - minHeight + 1;
        for (int i = 0; i < chancesToSpawn; i++) {
            int x = chunk_X * 16 + rand.nextInt(16);
            int y = minHeight + rand.nextInt(heightDiff);
            int z = chunk_Z * 16 + rand.nextInt(16);
            generator.generate(world, rand, new BlockPos(x, y, z));
        }
    }

}