[A] map: HashMap && ConcurrentHashMap && LinkedHashMap

Author: c-rainstorm

README.md

@@ -13,8 +13,7 @@
 
 ## 目录简介
 
-<h1>Directory Tree</h1><p>
-        <a href=".">.</a><br>
+<a href=".">.</a><br>
         ├── <a href="./README.md">README.md</a><br>
         ├── <a href="./algo/">algo</a><br>
         │   ├── <a href="./algo/leetcode-148-Sort-List(%E5%8D%95%E9%93%BE%E8%A1%A8%E6%8E%92%E5%BA%8F).md">leetcode-148-Sort-List(单链表排序).md</a><br>
@@ -55,10 +54,16 @@
         │   │   &nbsp;&nbsp;&nbsp; │   ├── <a href="./java/source-code/jdk/collection/list-linkedlist.md">list-linkedlist.md</a><br>
         │   │   &nbsp;&nbsp;&nbsp; │   ├── <a href="./java/source-code/jdk/collection/list-stack.md">list-stack.md</a><br>
         │   │   &nbsp;&nbsp;&nbsp; │   ├── <a href="./java/source-code/jdk/collection/list-vector.md">list-vector.md</a><br>
+        │   │   &nbsp;&nbsp;&nbsp; │   ├── <a href="./java/source-code/jdk/collection/map-concurrenthashmap.md">map-concurrenthashmap.md</a><br>
         │   │   &nbsp;&nbsp;&nbsp; │   ├── <a href="./java/source-code/jdk/collection/map-enummap.md">map-enummap.md</a><br>
-        │   │   &nbsp;&nbsp;&nbsp; │   └── <a href="./java/source-code/jdk/collection/map-identityhashmap.md">map-identityhashmap.md</a><br>
+        │   │   &nbsp;&nbsp;&nbsp; │   ├── <a href="./java/source-code/jdk/collection/map-hashmap.md">map-hashmap.md</a><br>
+        │   │   &nbsp;&nbsp;&nbsp; │   ├── <a href="./java/source-code/jdk/collection/map-identityhashmap.md">map-identityhashmap.md</a><br>
+        │   │   &nbsp;&nbsp;&nbsp; │   ├── <a href="./java/source-code/jdk/collection/map-linkedhashmap.md">map-linkedhashmap.md</a><br>
+        │   │   &nbsp;&nbsp;&nbsp; │   └── <a href="./java/source-code/jdk/collection/map-weakhashmap.md">map-weakhashmap.md</a><br>
         │   │   &nbsp;&nbsp;&nbsp; └── <a href="./java/source-code/jdk/lang/">lang</a><br>
-        │   │   &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; └── <a href="./java/source-code/jdk/lang/integer.md">integer.md</a><br>
+        │   │   &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; ├── <a href="./java/source-code/jdk/lang/integer.md">integer.md</a><br>
+        │   │   &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; └── <a href="./java/source-code/jdk/lang/ref/">ref</a><br>
+        │   │   &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; └── <a href="./java/source-code/jdk/lang/ref/reference.md">reference.md</a><br>
         │   ├── <a href="./java/test/">test</a><br>
         │   │   └── <a href="./java/test/awaitility.zh.md">awaitility.zh.md</a><br>
         │   ├── <a href="./java/%E5%9B%BE%E8%A7%A3JavaCollectionFramework.md">图解JavaCollectionFramework.md</a><br>

java/source-code/jdk/collection/map-concurrenthashmap.md

@@ -0,0 +1,7 @@
+# `ConcurrentHashMap<K,V>`
+
+看参考一篇吧，足够了。
+
+## 参考
+
+- [为并发而生的 ConcurrentHashMap（Java 8）](https://cloud.tencent.com/developer/article/1013643)

java/source-code/jdk/collection/map-hashmap.md

@@ -0,0 +1,55 @@
+# `HashMap<K,V>`
+
+## 设计
+
+链地址法，链上条目超过8个转红黑树。红黑树小于 6 退化成链。
+
+## 扩容策略
+
+```java
+/**
+    * The default initial capacity - MUST be a power of two.
+    */
+static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
+
+
+/**
+* The bin count threshold for using a tree rather than list for a
+* bin.  Bins are converted to trees when adding an element to a
+* bin with at least this many nodes. The value must be greater
+* than 2 and should be at least 8 to mesh with assumptions in
+* tree removal about conversion back to plain bins upon
+* shrinkage.
+*/
+static final int TREEIFY_THRESHOLD = 8;
+
+/**
+* The bin count threshold for untreeifying a (split) bin during a
+* resize operation. Should be less than TREEIFY_THRESHOLD, and at
+* most 6 to mesh with shrinkage detection under removal.
+*/
+static final int UNTREEIFY_THRESHOLD = 6;
+
+/**
+* The smallest table capacity for which bins may be treeified.
+* (Otherwise the table is resized if too many nodes in a bin.)
+* Should be at least 4 * TREEIFY_THRESHOLD to avoid conflicts
+* between resizing and treeification thresholds.
+*/
+static final int MIN_TREEIFY_CAPACITY = 64;
+```
+
+达到阈值直接扩容为原来两倍
+
+```java
+/**
+ * Initializes or doubles table size.  If null, allocates in
+ * accord with initial capacity target held in field threshold.
+ * Otherwise, because we are using power-of-two expansion, the
+ * elements from each bin must either stay at same index, or move
+ * with a power of two offset in the new table.
+ *
+ * @return the table
+ */
+final Node<K,V>[] resize() {}
+```

java/source-code/jdk/collection/map-linkedhashmap.md

@@ -0,0 +1,7 @@
+# `LinkedHashMap<K,V>`
+
+继承自 HashMap
+
+## 节点继承结构
+
+![collection-hashmap-node-class](http://image.rainstorm.vip/blog/collection-hashmap-node-class.png)

res/collection-hashmap-node-class.pu

@@ -0,0 +1,19 @@
+@startuml collection-hashmap-node-class
+
+
+interface Map.Entry<K,V>
+class HashMap.Node<K,V>
+class HashMap.TreeNode<K,V>
+class LinkedListHashMap.Entry<K,V>
+
+
+Map.Entry <.. HashMap.Node
+HashMap.Node <-- LinkedListHashMap.Entry
+LinkedListHashMap.Entry <-- HashMap.TreeNode
+
+
+caption hashmap节点继承结构类图
+
+right footer https://github.com/c-rainstorm/blog 转载请注明出处
+
+@enduml