public interface CallBack<T> {
    void onSuccess(T done);
    void onFailure(Throwable cause);
}

public void hasRecord(final CallBack<HashMap> callBack, final Player player) {
    Bukkit.getScheduler().runTaskAsynchronously(plugin, new Runnable() {
        @Override
        public void run() {
            final HashMap<String, Boolean> result = new HashMap<String, Boolean>();

            PreparedStatement q = connection.prepareStatement("SELECT * FROM " + tableName + " WHERE " + rowUsername + " = ? LIMIT 1");

            q.setString(1, player.getName());

            ResultSet resultat = q.executeQuery();
            boolean hasRecord = resultat.next();
            q.close();

            result.put("hasRecord", hasRecord);

            Bukkit.getScheduler().runTask(plugin, new Runnable() {
                @Override
                public void run() {
                    @Override
                    public void run() {
                        callBack.onSuccess(result);
                    }
                }
            });
        }
    });
}

public void test() {

    // Je veux recuperer si le hasRecord du joueur

    hasRecord(new CallBack<HashMap>() {

        @Override
        public void onSuccess(HashMap done) {
            boolean hasRecord = done.get("hasRecord");
        }

        @Override
        public void onFailure(Throwable cause) {
            System.out.println("ERROR: LOADING ASYNC MYSQL DATA");
        }

    }, p);

}