Dive | Bukkit

package com.TopicaRP.spenk.Dive;

import java.util.ArrayList;
import java.util.logging.Logger;

import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.EntityDamageEvent;
import org.bukkit.inventory.ItemStack;
import org.bukkit.plugin.java.JavaPlugin;

public class Dive extends JavaPlugin implements Listener{

    public String name = "Dive";
    public String author = "Spenk";
    public String version = "1.0.x";
    public Logger log = Logger.getLogger("Minecraft");

     public void onEnable() {
         getServer().getPluginManager().registerEvents(this, this);
         log.info(name+" by "+author+" version "+version+" is Enabled!");

     }

     public void onDisable() {

         log.info(name+" by "+author+" version "+version+" is Disabled!");

     }

        ArrayList<String> DivePlayers = new ArrayList<String>();

        @EventHandler
        public void onEntityDamage(EntityDamageEvent event) {
             if (!(event.getEntity() instanceof Player)){ return; }
             Player player = (Player)event.getEntity();
                if (event.getCause().equals(EntityDamageEvent.DamageCause.DROWNING) && DivePlayers.contains(player.getName()) && player.getInventory().getHelmet().getType() == Material.GLASS){
                    event.setCancelled(true);
                }
        }

        @EventHandler
        public boolean onCommand(CommandSender sender, Command cmd, String commandLabel, String[] args) {
            if (commandLabel.equalsIgnoreCase("Dive"))
            {
              if ((sender instanceof Player))
              {
                if ((sender.hasPermission("Dive.dive")) || (sender.isOp()))
                {
                    Player player = (Player)sender;

                  if (args.length == 0)
                  {
                      if (player.getItemInHand() != null){
                          if (player.getItemInHand().getType() != Material.GLASS){
                              player.sendMessage("§cYou need to hold a glassblock to dive!");
                              return true;
                          }
                      }

                      if (player.getInventory().getHelmet() != null){
                          player.sendMessage("§cThe helmet slot got to be empty!");
                          return true;
                      }

                      if (player.getInventory().getItemInHand().getAmount() == 1){
                          player.getInventory().remove(player.getItemInHand());
                          this.divePlayer(player);
                          player.sendMessage("§cYou put on your dive gear");
                          return true;
                      }

                      player.getItemInHand().setAmount(player.getItemInHand().getAmount() -1);
                      this.divePlayer(player);
                      player.sendMessage("§cYou put on your dive gear");
                      return true;
                  }
                }
              }
            }
            return false;
        }

        public void divePlayer(Player player){
            ItemStack i = new ItemStack(20,1);
            player.getInventory().setHelmet(i);
            DivePlayers.add(player.getName());
            return;
        }

}