Part 5: code section 1

//for part 5 in the series: http://forums.bukkit.org/threads/the-always-up-to-date-definitive-guide-to-terrain-generation-part-one-prerequisites-and-setup.93982/
public class BasicChunkGenerator extends ChunkGenerator {

    /**
     *
     * @param x
     * X co-ordinate of the block to be set in the array
     * @param y
     * Y co-ordinate of the block to be set in the array
     * @param z
     * Z co-ordinate of the block to be set in the array
     * @param chunk
     * An array containing the Block id's of all the blocks in the chunk. The first offset
     * is the block section number. There are 16 block sections, stacked vertically, each of which
     * 16 by 16 by 16 blocks.
     * @param material
     * The material to set the block to.
     */
    void setBlock(int x, int y, int z, byte[][] chunk, Material material) {
        //if the Block section the block is in hasn't been used yet, allocate it
        if (chunk[y >> 4] == null)
            chunk[y >> 4] = new byte[16 * 16 * 16];
        if (!(y <= 256 && y >= 0 && x <= 16 && x >= 0 && z <= 16 && z >= 0))
            return;
        try {
            chunk[y >> 4][((y & 0xF) << 8) | (z << 4) | x] = (byte) material
                    .getId();
        } catch (Exception e) {
            // do nothing
        }
    }

    @Override
    /**
     * @param world
     * The world the chunk belongs to
     * @param rand
     * Don't use this, make a new random object using the world seed (world.getSeed())
     * @param biome
     * Use this to set/get the current biome
     * @param ChunkX and ChunkZ
     * The x and z co-ordinates of the current chunk.
     */
    public byte[][] generateBlockSections(World world, Random rand, int ChunkX,
            int ChunkZ, BiomeGrid biome) {

        SimplexOctaveGenerator gen1 = new SimplexOctaveGenerator(world,8);
        gen1.setScale(1/32.0); //how "scaled" the noise generator should be.

        byte[][] chunk = new byte[world.getMaxHeight() / 16][];

        for (int x=0; x<16; x++) {
            for (int z=0; z<16; z++) {

                int realX = x + ChunkX * 16; //used so that the noise function gives us
                int realZ = z + ChunkZ * 16; //different values each chunk

                for (int y=64;y<128;y++) {
                    double density = gen1.noise(realX,y, realZ, 0.5, 0.5); //note 3d noise is VERY slow, I recommend using 2d noise to limit the number of 3d noise values that must be calculated.
                    double threshold = 0.0; //the noise function returns values between -1 and 1.
                    if (density > threshold) {
                        setBlock(x,y,z,chunk,Material.STONE);
                    }
                }
            }
        }
        return chunk;
    }
    /**
     * Returns a list of all of the block populators (that do "little" features)
     * to be called after the chunk generator
     */
    @Override
    public List<BlockPopulator> getDefaultPopulators(World world) {
        ArrayList<BlockPopulator> pops = new ArrayList<BlockPopulator>();
        //Add Block populators here
        return pops;
    }
}