如何在大量数据中找出第2大的数字

public TreeSet() {
    this(new TreeMap<E,Object>());
}

public TreeMap(Comparator<? super K> comparator) {
    this.comparator = comparator;
}

public V put(K key, V value) {
    Entry<K,V> t = root;
      ...
        do {
            parent = t;
            cmp = cpr.compare(key, t.key);
            if (cmp < 0)
                t = t.left;
            else if (cmp > 0)
                t = t.right;
            else
                return t.setValue(value);
        } while (t != null);
   ...
Entry<K,V> e = new Entry<>(key, value, parent);
    fixAfterInsertion(e);
   ...
}