LinkedHashMap 是如何保证有序的？

//map的遍历方法如下
  for (Map.Entry<String,Integer> entry : map.entrySet()) {
            System.out.println(entry.getKey()+":"+entry.getValue());
        }

HashMap#entrySet方法

//next逻辑如下

   final Node<K,V> nextNode() {
            Node<K,V>[] t;
            Node<K,V> e = next;
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            if (e == null)
                throw new NoSuchElementException();
//HashMap散列图、Hashtable散列表是按“有利于随机查找的散列(hash)的顺序”。并非按输入顺序。
            if ((next = (current = e).next) == null && (t = table) != null) {
                do {} while (index < t.length && (next = t[index++]) == null);
            }
            return e;
        }

LinkedHashMap 重写了entrySet方法

  public Set<Map.Entry<K,V>> entrySet() {
        Set<Map.Entry<K,V>> es;
        return (es = entrySet) == null ? (entrySet = new LinkedEntrySet()) : es;
    }

//next 逻辑,可以发现是按node的next指针进行遍历的
   final LinkedHashMap.Entry<K,V> nextNode() {
            LinkedHashMap.Entry<K,V> e = next;
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            if (e == null)
                throw new NoSuchElementException();
            current = e;
            next = e.after;
            return e;
        }