PotionMain

package me.AntonErlandsson.PotionEffects;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.configuration.file.FileConfiguration;
import org.bukkit.entity.Player;
import org.bukkit.event.Listener;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.inventory.meta.SkullMeta;
import org.bukkit.plugin.PluginDescriptionFile;
import org.bukkit.plugin.java.JavaPlugin;

import me.AntonErlandsson.PotionEffects.events.GUIHandler;
import me.AntonErlandsson.PotionEffects.events.UpdateMessage;
import me.AntonErlandsson.PotionEffects.handler.CommandManager;

public class PotionMain extends JavaPlugin implements Listener {
	public static PotionMain getPlugin(){
        return instancePlugin;
	}

	private static PotionMain instancePlugin;
    private static PotionMain instance;
    public CommandManager commandManager;
    PluginDescriptionFile plugin = this.getDescription();
    PotionMain main = this;

    private String currentVersion = plugin.getVersion();

    public boolean update;
    public static Inventory playerUI;

	@SuppressWarnings("unused")
	private UpdateMessage updatemessage = new UpdateMessage(this);

    public void onEnable() {
    	updateChecker.start();
        setInstance(this);
        commandManager = new CommandManager();

        commandManager.setup();

        final FileConfiguration config = this.getConfig();

		config.options().copyDefaults(true);
        saveDefaultConfig();

        instancePlugin = this;

        getServer().getPluginManager().registerEvents(new GUIHandler(main), this);

        getServer().getPluginManager().registerEvents(new UpdateMessage(main), this);

        getServer().getConsoleSender().sendMessage(ChatColor.AQUA + plugin.getName() + " is currently running on " + plugin.getVersion() + " by Anton Erlandsson");

    }
    public static void createInv(Player player) {

    	ArrayList<Player> player_list = new ArrayList<>(player.getServer().getOnlinePlayers());
		playerUI = Bukkit.createInventory(player, 54, ChatColor.DARK_PURPLE + "" + ChatColor.BOLD + "PotionEffects GUI");
		for (int i = 0;i < player_list.size();i++) {
			ItemStack playerHead = new ItemStack(Material.PLAYER_HEAD);
			SkullMeta skullMeta = (SkullMeta) playerHead.getItemMeta();
			skullMeta.setOwningPlayer(player_list.get(i));
			playerHead.setItemMeta(skullMeta);
			ItemMeta meta = playerHead.getItemMeta();
			meta.setDisplayName(ChatColor.LIGHT_PURPLE + "" + ChatColor.BOLD + player_list.get(i).getDisplayName());
			ArrayList<String> lore = new ArrayList<>();
			lore.add(ChatColor.GRAY + "Click to select player!");
			meta.setLore(lore);
			playerHead.setItemMeta(meta);
			playerUI.addItem(playerHead);
		}

    }

    public static PotionMain getInstance() {
        return instance;
    }

    private static void setInstance(PotionMain instance) {
        PotionMain.instance = instance;
    }

    Thread updateChecker = new Thread() {
    	@Override
    	public void run() {
    		URL url = null;
    		try {
    		    url = new URL("https://api.spigotmc.org/legacy/update.php?resource=70873");
    		} catch (MalformedURLException e) {
    		    e.printStackTrace();
    		}
    		URLConnection conn = null;
    		try {
    		    conn = url.openConnection();
    		} catch (IOException e) {
    		    e.printStackTrace();
    		}
    		try {
    		    BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
    		    if (reader.readLine().equals(currentVersion)) {
    		    	Bukkit.getScheduler().scheduleSyncDelayedTask(main, new Runnable() {

						@Override
						public void run() {
							if(PotionMain.getPlugin().getConfig().getBoolean("Check_Updates") == true) {
							getServer().getConsoleSender().sendMessage(ChatColor.GREEN + plugin.getName() + " is currently running on the latest version!");
							update = false;
							}
						}
    		    	}, 100L);
    		    } else {
    		    	Bukkit.getScheduler().scheduleSyncDelayedTask(main, new Runnable() {
						@Override
						public void run() {
							if(PotionMain.getPlugin().getConfig().getBoolean("Check_Updates") == true) {
							getServer().getConsoleSender().sendMessage(ChatColor.RED + plugin.getName() + " is not running on the latest version! Download the latest version on: https://www.spigotmc.org/resources/potioneffects.70873/");
							update = true;
							}
						}
    		    	}, 100L);
    		    }
    		} catch (IOException e) {
    		    e.printStackTrace();
    		}
    	}
    };
}