http://www.bukkit.fr/topic/19326-classer-des-joueurs-dune-mapplayer-integer-de-celui-poss%C3%A9dant-le-plus-gros-int-au-plus-petit/

Plugin.java

package fr.neatmonster.plugin;

import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;
import java.util.UUID;

import org.bukkit.ChatColor;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.EventPriority;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.PlayerDeathEvent;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.scoreboard.DisplaySlot;
import org.bukkit.scoreboard.Objective;
import org.bukkit.scoreboard.Scoreboard;

public class Plugin extends JavaPlugin implements Listener {
    private static <K, V extends Comparable<V>> Map<K, V> sortByValues(final Map<K, V> kMap) {
        final Map<K, V> vMap = new TreeMap<>(new Comparator<K>() {

            @Override
            public int compare(final K k1, final K k2) {
                final int k = kMap.get(k1).compareTo(kMap.get(k2));
                return k == 0 ? 1 : k;
            }
        });
        vMap.putAll(kMap);
        return vMap;
    }

    private final Map<UUID, Integer> kills = new HashMap<>();

    @Override
    public void onEnable() {
        getServer().getPluginManager().registerEvents(this, this);
        getServer().getScheduler().scheduleSyncRepeatingTask(this, new Runnable() {
            Scoreboard board;

            @Override
            public void run() {
                if (board == null)
                    board = getServer().getScoreboardManager().getNewScoreboard();

                for (final String entry : board.getEntries())
                    board.resetScores(entry);

                Objective obj = board.getObjective("kills");
                if (obj == null) {
                    obj = board.registerNewObjective("kills", "dummy");
                    obj.setDisplayName(ChatColor.GOLD + "Kills");
                    obj.setDisplaySlot(DisplaySlot.SIDEBAR);
                }

                for (final Entry<UUID, Integer> entry : new LinkedList<>(
                        sortByValues(kills).entrySet()).subList(0, 3))
                    obj.getScore(getServer().getPlayer(entry.getKey())
                            .getPlayerListName()).setScore(entry.getValue());

                for (final Player player : getServer().getOnlinePlayers())
                    player.setScoreboard(board);
            }
        }, 0L, 20L);
    }

    @EventHandler(priority = EventPriority.MONITOR)
    public void onPlayerDeath(final PlayerDeathEvent event) {
        if (event.getEntity().getKiller() == null)
            return;
        final UUID killer = event.getEntity().getKiller().getUniqueId();
        if (!kills.containsKey(killer))
            kills.put(killer, 0);
        kills.put(killer, kills.get(killer) + 1);
    }
}