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crossoverJiecrossoverJie
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💬 update LinkedHashMap
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‎MD/collection/LinkedHashMap.md‎

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调试可以看到 `map` 的组成：
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![](https://ws2.sinaimg.cn/large/006tKfTcly1fo6l9xp91lj319m0s4tgi.jpg)
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打开源码可以看到：
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```java
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/**
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* The head of the doubly linked list.
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*/
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private transient Entry<K,V> header;
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/**
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* The iteration ordering method for this linked hash map: <tt>true</tt>
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* for access-order, <tt>false</tt> for insertion-order.
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*
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* @serial
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*/
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private final boolean accessOrder;
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private static class Entry<K,V> extends HashMap.Entry<K,V> {
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// These fields comprise the doubly linked list used for iteration.
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Entry<K,V> before, after;
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Entry(int hash, K key, V value, HashMap.Entry<K,V> next) {
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super(hash, key, value, next);
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}
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}
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```
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其中 `Entry` 继承于 `HashMap` 的 `Entry`，并新增了上下节点的指针，也就形成了双向链表。
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还有一个 header 的成员变量，是这个双向链表的头结点。

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