World generator doesn't generate?

I've written a world generator which generates a volcano.

Code:

package me.baummann.plugins.volcanoes;

import java.util.Random;
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.World;
import org.bukkit.block.Block;

public class VolcanoGen {
    private int blocks = 0;
    private boolean generated = false;
    public boolean generate(World world, Random random, int i, int j, int k) {
        if (world.getBlockAt(i, j - 1, k).getType() == Material.AIR || world.getBlockAt(i, j + 1, k).getType() != Material.AIR) {
            return false;
        }

        int radius = 30;
        int height = 0;
        for (int l = 0; l < 20; l++) {
            radius--;
            height++;
            generateDisc(radius, height, new Location(world, i, j, k), Material.STONE, random);
        }

        radius = 29;
        height = 0;
        for (int l = 0; l < 20; l++) {
            radius--;
            height++;
            generateDisc(radius, height, new Location(world, i, j, k), Material.LAVA, random);
        }
        generated = true;
        return true;
    }

    public boolean hasGenerated() {
        return generated;
    }

    public int blocksUsed() {
        return blocks;
    }

    public void generateDisc(int radius, int height, Location loc, Material mat, Random rand) {
        for (int x = -radius; x <= radius; x++) {
            for (int z = -radius; z <= radius; z++) {
                for (int y = 0; y <= height; y++) {
                    if (x * x + z * z < radius) {
                        if (mat == Material.LAVA) {
                            setBlock(new Location(loc.getWorld(), loc.getX() + x + rand.nextInt(3), y, loc.getZ() + z + rand.nextInt(3)), mat);
                            continue;
                        }
                        int kindOfMovement = rand.nextInt(4);
                        if (kindOfMovement == 0) {
                            setBlock(new Location(loc.getWorld(), loc.getX() + x + rand.nextInt(3), y, loc.getZ() + z + rand.nextInt(3)), mat);
                        } else if (kindOfMovement == 1) {
                            setBlock(new Location(loc.getWorld(), loc.getX() + x - rand.nextInt(3), y, loc.getZ() + z - rand.nextInt(3)), mat);
                        } else if (kindOfMovement == 2) {
                            setBlock(new Location(loc.getWorld(), loc.getX() + x + rand.nextInt(3), y, loc.getZ() + z - rand.nextInt(3)), mat);
                        } else if (kindOfMovement == 3) {
                            setBlock(new Location(loc.getWorld(), loc.getX() + x - rand.nextInt(3), y, loc.getZ() + z + rand.nextInt(3)), mat);
                        } else {
                            setBlock(new Location(loc.getWorld(), loc.getX() + x - rand.nextInt(3), y, loc.getZ() + z - rand.nextInt(3)), mat);
                        }
                    }
                }
            }
        }
    }

    private void setBlock(Location loc, Material material) {
        Block block = loc.getBlock();
        block.setType(material);
        block.getState().update(true);
        blocks++;
    }
}

Code:

package me.baummann.plugins.volcanoes;

import java.util.Random;
import org.bukkit.Bukkit;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;

public class VolcanoCommand implements CommandExecutor {
    private Volcanoes plugin;
    public VolcanoCommand(Volcanoes instance) {
        plugin = instance;
    }

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String cmdLine, String[] split) {
        if (!(sender instanceof Player)) {
            msg(sender, "&cCan't use that in console!");
            return true;
        }

        final Player player = (Player) sender;
        if (!player.hasPermission("volcanoes.volcano")) {
            msg(player, "&cNo permission!");
            return true;
        }

        Bukkit.getServer().broadcastMessage("Lag incoming!");

        VolcanoGen gen = new VolcanoGen();
        gen.generate(player.getWorld(), new Random(), player.getLocation().getBlockX(), player.getLocation().getBlockY(), player.getLocation().getBlockZ());
        msg(player, "&2Generation finished!");
        return true;
    }

    public void msg(CommandSender sender, String msg) {
        String parsedMessage = msg.replace('&', '\u00A7');
        sender.sendMessage(parsedMessage);
    }
}

When I use /volcano, it shows "Generation finished!" but nothing else happens. No lag, no volcano just text.

 

Your method generate(...) will always return false if you use the player's coordinates.
As far as I know, the eye height of the player will be used. That means the block below the eye height is always air, so your method returns false with that check.

if (world.getBlockAt(i, j - 1, k).getType() == Material.AIR || world.getBlockAt(i, j + 1, k).getType() != Material.AIR) { return false; }

 

Client side, the player position is the eye height. Server side the player position is the player's legs.
That's not the problem. I tried to use

Code:

if (!gen.generate(...)) {
player.sendMessage("Can't generate here!");
} else {
player.sendMessage("Generation finished!");
}

before which worked like a charm.