TreeMap

 public V put(K key, V value) {
        Entry<K,V> t = root;
　　　　　//根节点
        if (t == null) {
            compare(key, key); // type (and possibly null) check

            root = new Entry<>(key, value, null);
            size = 1;
            modCount++;
            return null;
        }

        int cmp;
        Entry<K,V> parent;
        // split comparator and comparable paths
        Comparator<? super K> cpr = comparator;
        if (cpr != null) {
　　　　　//比较器不为null的话，通过比较器进行比较寻找插入位置
            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);
        }
        else {
　　　　　　　//比较器为空的话，通过key的compare方法比较
            if (key == null)
                throw new NullPointerException();
            @SuppressWarnings("unchecked")
                Comparable<? super K> k = (Comparable<? super K>) key;
            do {
                parent = t;
                cmp = k.compareTo(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);
　　　　　//插入树中
        if (cmp < 0)
            parent.left = e;
        else
            parent.right = e;
　　　　//进行红黑树重平衡
        fixAfterInsertion(e);
        size++;
        modCount++;
        return null;
    }