Main class code for world gen: 
GameRegistry.registerWorldGenerator(new WorldGeneratorEndless()); 
  
World gen class: 
package endless.common; 
  
import java.util.Random; 
  
import net.minecraft.world.World; 
import net.minecraft.world.chunk.IChunkProvider; 
import net.minecraft.world.gen.feature.WorldGenMinable; 
import cpw.mods.fml.common.IWorldGenerator; 
  
public class WorldGeneratorEndless implements IWorldGenerator { 
  
@Override 
public void generate(Random random, int chunkX, int chunkZ, World world, IChunkProvider chunkGenerator, IChunkProvider chunkProvider) { 
  
switch(world.provider.dimensionId) { 
  
case -1: 
generateNether(world, random, chunkX * 16, chunkZ * 16); 
case 0: 
generateSurface(world, random, chunkX * 16, chunkZ * 16); 
case 1: 
generateEnd(world, random, chunkX * 16, chunkZ * 16); 
} 
  
} 
  
private void generateNether(World world, Random random, int blockX, int blockZ) { 
  
} 
  
private void generateSurface(World world, Random random, int blockX, int blockZ) { 
  
} 
  
public int i; 
  
public int Xcoord; 
public int Ycoord; 
public int Zcoord; 
  
private void generateEnd(World world, Random random, int blockX, int blockZ) { 
  
for (int i = 0; i < 8; i++) { 
  
int Xcoord = blockX + random.nextInt(16); 
int Ycoord = random.nextInt(56); 
int Zcoord = blockZ + random.nextInt(16); 
  
(new WorldGenMinable(Endless.AncientOre.blockID, ).generate(world, random, Xcoord, Ycoord, Zcoord); 
} 
} 
} 
Not in code: 
Smily face is supposed to be eight