FreezeFactory from Hell v1.1 - Bukkit

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

import org.bukkit.Location;
import org.bukkit.block.Block;
import org.bukkit.block.BlockFace;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerToggleSprintEvent;
import org.bukkit.plugin.Plugin;
import org.bukkit.potion.PotionEffect;
import org.bukkit.potion.PotionEffectType;
import org.bukkit.scheduler.BukkitRunnable;

/**
 * FreezeFactory from Hell - v1.1
 * @author ArthurMaker
 * Greetings from Brazil, gentlemen!
 */
public class FreezeFactory implements Listener {

    private Plugin plugin;
    private static List<UUID> players = new ArrayList<UUID>();

    public FreezeFactory (Plugin plugin){
        this.plugin = plugin;
        this.plugin.getServer().getPluginManager().registerEvents(this, this.plugin);
    }

    /**
     * Freezes a player.
     */
    public void freezePlayer(Player p){
        if(isFrozen(p)) return;
        p.setWalkSpeed(0F);
        p.setFallDistance(0F);
        p.teleport(this.getGround(p));
        p.addPotionEffect(new PotionEffect(PotionEffectType.JUMP, Integer.MAX_VALUE, -127));
        players.add(p.getUniqueId());
    }

    /**
     * Unfreezes a player.
     */
    public void unfreezePlayer(Player p){
        if(!isFrozen(p)) return;
        p.removePotionEffect(PotionEffectType.JUMP);
        p.setWalkSpeed(0.2F); // normal speed
        players.remove(p.getUniqueId());
    }

    private Location getGround(Player p){
        Block relative = p.getLocation().getBlock().getRelative(BlockFace.DOWN);
        for(int i = 0; i < 256; i++){
            if(relative.getType().isOccluding()){
                Location b = relative.getRelative(BlockFace.UP).getLocation();
                return new Location(b.getWorld(), b.getX(), b.getY(), b.getZ(), p.getEyeLocation().getYaw(), p.getEyeLocation().getPitch()).add(0.5, 0, 0.5);
            }else{
                relative = relative.getRelative(BlockFace.DOWN);
            }
        }
        return p.getLocation();
    }

    /**
     * Check if a player is frozen.
     */
    public boolean isFrozen(Player p){
        return players.contains(p.getUniqueId());
    }

    @EventHandler
    public void onSprint(PlayerToggleSprintEvent event){
        final Player p = event.getPlayer();
        if(isFrozen(p)){
            new BukkitRunnable(){
                @Override
                public void run() {
                    if(p.isSprinting()){
                        p.teleport(p);
                    }else{
                        this.cancel();
                    }
                }
            }.runTaskTimer(this.plugin, 0L, 1L);
        }
    }

}