public V put(K key, V value) {

    Entry<K,V> t = root; //得到根节点

    if (t == null) { //如果根节点为空

        compare(key, key); // type (and possibly null) check

        root = new Entry<>(key, value, null); //把当前的键值对插入作为根节点

        size = 1;

        modCount++;

        return null;

    }

    int cmp;

    Entry<K,V> parent;

    // split comparator and comparable paths

    Comparator<? super K> cpr = comparator; //取得比较器

    if (cpr != null) {

        do {

            parent = t;

            cmp = cpr.compare(key, t.key); //根据比较器 比较当前节点与插入节点的key

            if (cmp < 0) //如果当前节点较小

                t = t.left;

            else if (cmp > 0) //如果当前节点较大

                t = t.right;

            else //如果相同

                return t.setValue(value);

        } while (t != null);

    }

    else { //如果没有传入一个比较器

        if (key == null)

            throw new NullPointerException();

        @SuppressWarnings("unchecked")

            Comparable<? super K> k = (Comparable<? super K>) key; //尝试将key转为Comparable<? super K>类型，就是说 如果没有传入比较器

                                                    //，key所在的类需要实现Comparable接口

        do {

            parent = t;

            cmp = k.compareTo(t.key); //尝试用key自己实现的comparteTo方法比较父节点的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); //创建新节点，设置key value 父节点

    if (cmp < 0)

        parent.left = e;

    else

        parent.right = e;

    fixAfterInsertion(e); //插入新节点后 对 红黑树继续宁

    size++;

    modCount++;

    return null;

}

public V put(K key, V value) {

    Entry<K,V> t = root; //得到根节点

    if (t == null) { //如果根节点为空

        compare(key, key); // type (and possibly null) check

        root = new Entry<>(key, value, null); //把当前的键值对插入作为根节点

        size = 1;

        modCount++;

        return null;

    }

    int cmp;

    Entry<K,V> parent;

    // split comparator and comparable paths

    Comparator<? super K> cpr = comparator; //取得比较器

    if (cpr != null) {

        do {

            parent = t;

            cmp = cpr.compare(key, t.key); //根据比较器 比较当前节点与插入节点的key

            if (cmp < 0) //如果当前节点较小

                t = t.left;

            else if (cmp > 0) //如果当前节点较大

                t = t.right;

            else //如果相同

                return t.setValue(value);

        } while (t != null);

    }

    else { //如果没有传入一个比较器

       if (key == null)

        throw new NullPointerException();

    @SuppressWarnings("unchecked")

    //尝试将key转为Comparable ，如果没有实现此接口，会报错

        Comparable<? super K> k = (Comparable<? super K>) key;

    do {

        parent = t;

        cmp = k.compareTo(t.key);//尝试用key自身的compareTo方法比较

        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); //此时，找到插入的位置，创建新的节点，传入参数，以及对父节点的引用

if (cmp < 0)

    parent.left = e;

else

    parent.right = e;

fixAfterInsertion(e); //插入节点后，对红黑树进行相应的变化

size++;

modCount++;

return null;