auto commit

2018-02-28 15:50:25 +08:00
parent d5dda714db
commit db5a16d39d
17 changed files with 4686 additions and 4669 deletions
--- a/notes/Java
+++ b/notes/Java
@ -1,78 +1,79 @@
 <!-- GFM-TOC -->
-* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#<EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
+* [概览](#概览)
    * [1. List](#1-list)
    * [2. Set](#2-set)
    * [3. Queue](#3-queue)
    * [4. Map](#4-map)
-    * [5. Java 1.0/1.1 <EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#5-java-1011-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
-* [<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ](#<23><><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><D0B5><EFBFBD><EFBFBD><EFBFBD>ģʽ)
-    * [1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ](#1-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ)
-    * [2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ](#2-<2D><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ)
-* [ɢ<EFBFBD><EFBFBD>](#ɢ<EFBFBD><EFBFBD>)
-* [Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#Դ<><D4B4><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)
+    * [5. Java 1.0/1.1 容器](#5-java-1011-容器)
+* [容器中的设计模式](#容器中的设计模式)
+    * [1. 迭代器模式](#1-迭代器模式)
+    * [2. 适配器模式](#2-适配器模式)
+* [散列](#散列)
+* [源码分析](#源码分析)
    * [1. ArraList](#1-arralist)
-    * [2. Vector <EFBFBD><EFBFBD> Stack](#2-vector-<EFBFBD><EFBFBD>-stack)
+    * [2. Vector 与 Stack](#2-vector-与-stack)
    * [3. LinkedList](#3-linkedlist)
    * [4. TreeMap](#4-treemap)
    * [5. HashMap](#5-hashmap)
    * [6. LinkedHashMap](#6-linkedhashmap)
    * [7. ConcurrentHashMap](#7-concurrenthashmap)
-* [<EFBFBD>ο<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>](#<23>ο<EFBFBD><CEBF><EFBFBD><EFBFBD><EFBFBD>)
+* [参考资料](#参考资料)
 <!-- GFM-TOC -->

-# <20><><EFBFBD><EFBFBD>

-![](https://github.com/CyC2018/InterviewNotes/blob/master/pics/ebf03f56-f957-4435-9f8f-0f605661484d.jpg)
+# 概览

-<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> Collection <20><> Map <20><><EFBFBD>֣<EFBFBD>Collection <20>ְ<EFBFBD><D6B0><EFBFBD><EFBFBD><EFBFBD> List<73><74>Set <20>Լ<EFBFBD> Queue<75><65>
+![](https://github.com/CyC2018/InterviewNotes/blob/master/pics//ebf03f56-f957-4435-9f8f-0f605661484d.jpg)
+
+容器主要包括 Collection 和 Map 两种，Collection 又包含了 List、Set 以及 Queue。

 ## 1. List

- ArrayList<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڶ<EFBFBD>̬<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>֣<EFBFBD>֧<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʣ<EFBFBD>
+- ArrayList：基于动态数组实现，支持随机访问；

- LinkedList<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>˫<EFBFBD><EFBFBD>ѭ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>֣<EFBFBD>ֻ<EFBFBD><EFBFBD>˳<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǿ<EFBFBD><EFBFBD>Կ<EFBFBD><EFBFBD>ٵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>м<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɾ<EFBFBD><EFBFBD>Ԫ<EFBFBD>ء<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ˣ<EFBFBD>LinkedList <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ջ<EFBFBD><D5BB><EFBFBD><EFBFBD><EFBFBD>к<EFBFBD>˫<EFBFBD>˶<EFBFBD><CBB6>С<EFBFBD>
+- LinkedList：基于双向循环链表实现，只能顺序访问，但是可以快速地在链表中间插入和删除元素。不仅如此，LinkedList 还可以用作栈、队列和双端队列。

 ## 2. Set

- HashSet<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> Hash ʵ<>֣<EFBFBD>֧<EFBFBD>ֿ<EFBFBD><D6BF>ٲ<EFBFBD><D9B2>ң<EFBFBD><D2A3><EFBFBD><EFBFBD><EFBFBD>ʧȥ<CAA7><C8A5><EFBFBD><EFBFBD><EFBFBD>ԣ<EFBFBD>
+- HashSet：基于 Hash 实现，支持快速查找，但是失去有序性；

- TreeSet<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ں<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>֣<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>򣬵<EFBFBD><EFBFBD>ǲ<EFBFBD><EFBFBD><EFBFBD>Ч<EFBFBD>ʲ<EFBFBD><EFBFBD><EFBFBD> HashSet<EFBFBD><EFBFBD>
+- TreeSet：基于红黑树实现，保持有序，但是查找效率不如 HashSet；

- LinkedListHashSet<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> HashSet <EFBFBD>Ĳ<EFBFBD><EFBFBD><EFBFBD>Ч<EFBFBD>ʣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڲ<EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ά<EFBFBD><EFBFBD>Ԫ<EFBFBD>صĲ<EFBFBD><EFBFBD><EFBFBD>˳<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>˾<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ԡ<EFBFBD>
+- LinkedListHashSet：具有 HashSet 的查找效率，且内部使用链表维护元素的插入顺序，因此具有有序性。

 ## 3. Queue

-ֻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>֣<EFBFBD>LinkedList <EFBFBD><EFBFBD> PriorityQueue<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> LinkedList ֧<EFBFBD><EFBFBD>˫<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>У<EFBFBD>PriorityQueue <EFBFBD>ǻ<EFBFBD><EFBFBD>ڶѽṹʵ<EFBFBD>֡<EFBFBD>
+只有两个实现：LinkedList 和 PriorityQueue，其中 LinkedList 支持双向队列，PriorityQueue 是基于堆结构实现。

 ## 4. Map

- HashMap<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> Hash ʵ<EFBFBD><EFBFBD>
+- HashMap：基于 Hash 实现

- LinkedHashMap<EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ά<EFBFBD><EFBFBD>Ԫ<EFBFBD>ص<EFBFBD>˳<EFBFBD><EFBFBD><EFBFBD><EFBFBD>˳<EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>˳<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD>ã<EFBFBD>LRU<EFBFBD><EFBFBD>˳<EFBFBD><EFBFBD>
+- LinkedHashMap：使用链表来维护元素的顺序，顺序为插入顺序或者最近最少使用（LRU）顺序

- TreeMap<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ں<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD><EFBFBD>
+- TreeMap：基于红黑树实现

- ConcurrentHashMap<EFBFBD><EFBFBD><EFBFBD>̰߳<EFBFBD>ȫ Map<61><70><EFBFBD><EFBFBD><EFBFBD>漰<EFBFBD><E6BCB0><EFBFBD><EFBFBD><EFBFBD><EFBFBD> HashTable <EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+- ConcurrentHashMap：线程安全 Map，不涉及类似于 HashTable 的同步加锁

-## 5. Java 1.0/1.1 <EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+## 5. Java 1.0/1.1 容器

-<EFBFBD><EFBFBD><EFBFBD>ھɵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ǿ<EFBFBD><EFBFBD><EFBFBD>Ӧ<EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǣ<EFBFBD>ֻ<EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>˽⡣
+对于旧的容器，我们决不应该使用它们，只需要对它们进行了解。

- Vector<EFBFBD><EFBFBD><EFBFBD><EFBFBD> ArrayList <EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̰߳<EFBFBD>ȫ<EFBFBD><EFBFBD>
+- Vector：和 ArrayList 类似，但它是线程安全的

- HashTable<EFBFBD><EFBFBD><EFBFBD><EFBFBD> HashMap <EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>̰߳<EFBFBD>ȫ<EFBFBD><EFBFBD>
+- HashTable：和 HashMap 类似，但它是线程安全的

-# <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ
+# 容器中的设计模式

-## 1. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ
+## 1. 迭代器模式

-<EFBFBD>Ӹ<EFBFBD><EFBFBD><EFBFBD>ͼ<EFBFBD><EFBFBD><EFBFBD>Կ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>඼<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD> Iterator <20><><EFBFBD>󣬿<EFBFBD><F3A3ACBF><EFBFBD>ͨ<EFBFBD><CDA8><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD>Ԫ<EFBFBD>ء<EFBFBD>
+从概览图可以看到，每个集合类都有一个 Iterator 对象，可以通过这个迭代器对象来遍历集合中的元素。

-[Java <EFBFBD>еĵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ ](https://github.com/CyC2018/InterviewNotes/blob/master/notes/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F.md#92-java-%E5%86%85%E7%BD%AE%E7%9A%84%E8%BF%AD%E4%BB%A3%E5%99%A8)
+[Java 中的迭代器模式 ](https://github.com/CyC2018/InterviewNotes/blob/master/notes/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F.md#92-java-%E5%86%85%E7%BD%AE%E7%9A%84%E8%BF%AD%E4%BB%A3%E5%99%A8)

-## 2. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ģʽ
+## 2. 适配器模式

-java.util.Arrays#asList() <EFBFBD><EFBFBD><EFBFBD>԰<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ת<EFBFBD><EFBFBD>Ϊ List <EFBFBD><EFBFBD><EFBFBD>͡<EFBFBD>
+java.util.Arrays#asList() 可以把数组类型转换为 List 类型。

 ```java
 List list = Arrays.asList(1, 2, 3);
@ -80,44 +81,44 @@ java.util.Arrays#asList()
 list = Arrays.asList(arr);
 ```

-# ɢ<EFBFBD><EFBFBD>
+# 散列

-ʹ<EFBFBD><EFBFBD> hasCode() <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɢ<EFBFBD><EFBFBD>ֵ<EFBFBD><EFBFBD>ʹ<EFBFBD>õ<EFBFBD><EFBFBD>Ƕ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ĵ<EFBFBD>ַ<EFBFBD><EFBFBD>
+使用 hasCode() 来返回散列值，使用的是对象的地址。

-<EFBFBD><EFBFBD> equals() <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȵģ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɢ<EFBFBD><EFBFBD>ֵһ<EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɢ<EFBFBD><EFBFBD>ֵ<EFBFBD><EFBFBD>ͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȡ<EFBFBD>
+而 equals() 是用来判断两个对象是否相等的，相等的两个对象散列值一定要相同，但是散列值相同的两个对象不一定相等。

-<EFBFBD><EFBFBD><EFBFBD>ȱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʣ<EFBFBD>
+相等必须满足以下五个性质：

-1. <EFBFBD>Է<EFBFBD><EFBFBD><EFBFBD>
-2. <EFBFBD>Գ<EFBFBD><EFBFBD><EFBFBD>
-3. <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
-4. һ<EFBFBD><EFBFBD><EFBFBD>ԣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ε<EFBFBD><EFBFBD><EFBFBD> x.equals(y)<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>䣩
-5. <EFBFBD><EFBFBD><EFBFBD>κβ<EFBFBD><EFBFBD><EFBFBD> null <20>Ķ<EFBFBD><C4B6><EFBFBD> x <20><><EFBFBD><EFBFBD> x.equals(nul) <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ false
+1. 自反性
+2. 对称性
+3. 传递性
+4. 一致性（多次调用 x.equals(y)，结果不变）
+5. 对任何不是 null 的对象 x 调用 x.equals(nul) 结果都为 false

-# Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+# 源码分析

-<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ķ<EFBFBD> [ <EFBFBD>㷨 - <EFBFBD><EFBFBD><EFBFBD><EFBFBD> ](https://github.com/CyC2018/InterviewNotes/blob/master/notes/%E7%AE%97%E6%B3%95.md#%E7%AC%AC%E4%B8%89%E7%AB%A0-%E6%9F%A5%E6%89%BE) <EFBFBD><EFBFBD><EFBFBD>֣<EFBFBD><EFBFBD>Լ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>кܴ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+建议先阅读 [ 算法 - 查找 ](https://github.com/CyC2018/InterviewNotes/blob/master/notes/%E7%AE%97%E6%B3%95.md#%E7%AC%AC%E4%B8%89%E7%AB%A0-%E6%9F%A5%E6%89%BE) 部分，对集合类源码的理解有很大帮助。

-Դ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>أ<EFBFBD>[OpenJDK 1.7](http://download.java.net/openjdk/jdk7)
+源码下载：[OpenJDK 1.7](http://download.java.net/openjdk/jdk7)

 ## 1. ArraList

 [ArraList.java](https://github.com/CyC2018/InterviewNotes/blob/master/notes/src/ArrayList.java)

-ʵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> RandomAccess <EFBFBD>ӿڣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>֧<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ȼ<EFBFBD>ģ<EFBFBD><EFBFBD><EFBFBD>Ϊ ArrayList <20>ǻ<EFBFBD><C7BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>ֵġ<D6B5>
+实现了 RandomAccess 接口，因此支持随机访问，这是理所当然的，因为 ArrayList 是基于数组实现的。

 ```java
 public class ArrayList<E> extends AbstractList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable
 ```

-<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>֣<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ԫ<EFBFBD>ص<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD> transient <20><><EFBFBD>Σ<EFBFBD><CEA3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><CEAA><EFBFBD><EFBFBD><EFBFBD>鲻һ<E9B2BB><D2BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD>ö<EFBFBD>ռ<EFBFBD><D5BC>Ԫ<EFBFBD>أ<EFBFBD><D8A3><EFBFBD><EFBFBD><EFBFBD>Ҳ<EFBFBD><D2B2>û<EFBFBD><C3BB>Ҫȫ<D2AA><C8AB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD><D0BB><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><D2AA>д writeObject() <EFBFBD><EFBFBD> readObject()<EFBFBD><EFBFBD>
+基于数组实现，保存元素的数组使用 transient 修饰，这是因为该数组不一定所有位置都占满元素，因此也就没必要全部都进行序列化。需要重写 writeObject() 和 readObject()。

 ```java
 private transient Object[] elementData;
 ```

-<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ĭ<EFBFBD>ϴ<EFBFBD>СΪ 10
+数组的默认大小为 10

 ```java
 public ArrayList(int initialCapacity) {
@ -132,7 +133,7 @@ public ArrayList() {
 }
 ```

-ɾ<EFBFBD><EFBFBD>Ԫ<EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> System.arraycopy() <EFBFBD><EFBFBD>Ԫ<EFBFBD>ؽ<EFBFBD><EFBFBD>и<EFBFBD><EFBFBD>ƣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɾ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɱ<EFBFBD><EFBFBD>ܸߣ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڴ<EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD>ָ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ŵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>С<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ٸ<EFBFBD><EFBFBD>Ʋ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ִ<EFBFBD>д<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+删除元素时调用 System.arraycopy() 对元素进行复制，因此删除操作成本很高，最好在创建时就指定大概的容量大小，减少复制操作的执行次数。

 ```java
 public E remove(int index) {
@ -150,9 +151,9 @@ public E remove(int index) {
 }
 ```

-<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ԫ<EFBFBD><EFBFBD>ʱʹ<EFBFBD><EFBFBD> ensureCapacity() <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>֤<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㹻<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݣ<EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 1.5 <EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+添加元素时使用 ensureCapacity() 方法来保证容量足够，如果不够时，需要进行扩容，使得新容量为旧容量的 1.5 倍。

-modCount <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>¼ ArrayList <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>仯<EFBFBD>Ĵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊÿ<EFBFBD><EFBFBD><EFBFBD>ڽ<EFBFBD><EFBFBD><EFBFBD> add() <EFBFBD><EFBFBD> addAll() ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> ensureCapacity()<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> ensureCapacity() <EFBFBD>ж<EFBFBD> modCount <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>޸ġ<EFBFBD>
+modCount 用来记录 ArrayList 发生变化的次数，因为每次在进行 add() 和 addAll() 时都需要调用 ensureCapacity()，因此直接在 ensureCapacity() 中对 modCount 进行修改。

 ```java
 public void ensureCapacity(int minCapacity) {
@ -190,7 +191,7 @@ private static int hugeCapacity(int minCapacity) {
 }
 ```

-<EFBFBD>ڽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ߵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ȳ<EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD>Ƚϲ<EFBFBD><EFBFBD><EFBFBD>ǰ<EFBFBD><EFBFBD> modCount <20>Ƿ<EFBFBD><C7B7>ı䣬<C4B1><E4A3AC><EFBFBD><EFBFBD><EFBFBD>ı<EFBFBD><C4B1><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD>׳<EFBFBD> ConcurrentModificationException<EFBFBD><EFBFBD>
+在进行序列化或者迭代等操作时，需要比较操作前后 modCount 是否改变，如果改变了需要抛出 ConcurrentModificationException。

 ```java
 private void writeObject(java.io.ObjectOutputStream s)
@ -213,20 +214,20 @@ private void writeObject(java.io.ObjectOutputStream s)
 }
 ```

-**<EFBFBD><EFBFBD> Vector <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>**
+**和 Vector 的区别**

-1.  Vector <EFBFBD><EFBFBD> ArrayList <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȫ<EFBFBD><EFBFBD>ͬ<EFBFBD>ģ<EFBFBD>Ψһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> Vector <20><>ͬ<EFBFBD><CDAC><EFBFBD>ģ<EFBFBD><C4A3><EFBFBD><EFBFBD>˿<EFBFBD><CBBF><EFBFBD><EFBFBD>ͱ<EFBFBD> ArrayList Ҫ<>󣬷<EFBFBD><F3A3ACB7><EFBFBD>Ҫ<EFBFBD><D2AA><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD><CAB9> ArrayList <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> Vector<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊͬ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɳ<EFBFBD><EFBFBD><EFBFBD>Ա<EFBFBD>Լ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ƣ<EFBFBD>
-2.  Vector ÿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>С<EFBFBD><EFBFBD> 2 <20><><EFBFBD>ռ䣬<D5BC><E4A3AC> ArrayList <EFBFBD><EFBFBD> 1.5 <EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+1.  Vector 和 ArrayList 几乎是完全相同的，唯一的区别在于 Vector 是同步的，因此开销就比 ArrayList 要大，访问要慢。最好使用 ArrayList 而不是 Vector，因为同步完全可以由程序员自己来控制；
+2.  Vector 每次扩容请求其大小的 2 倍空间，而 ArrayList 是 1.5 倍。

-Ϊ<EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD>̰߳<EFBFBD>ȫ<EFBFBD><EFBFBD> ArrayList<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD> Collections.synchronizedList(new ArrayList<>()); <EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD>̰߳<EFBFBD>ȫ<EFBFBD><EFBFBD> ArrayList<73><74>Ҳ<EFBFBD><D2B2><EFBFBD><EFBFBD>ʹ<EFBFBD><CAB9> concurrent <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>µ<EFBFBD> CopyOnWriteArrayList <EFBFBD>ࣻ
+为了使用线程安全的 ArrayList，可以使用 Collections.synchronizedList(new ArrayList<>()); 返回一个线程安全的 ArrayList，也可以使用 concurrent 并发包下的 CopyOnWriteArrayList 类；

-**<EFBFBD><EFBFBD> LinkedList <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>**
+**和 LinkedList 的区别**

-1.  ArrayList <EFBFBD><EFBFBD><EFBFBD>ڶ<EFBFBD>̬<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>֣<EFBFBD>LinkedList <20><><EFBFBD><EFBFBD>˫<EFBFBD><CBAB>ѭ<EFBFBD><D1AD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD>֣<EFBFBD>
-2. ArrayList ֧<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʣ<EFBFBD>LinkedList <EFBFBD><EFBFBD>֧<EFBFBD>֣<EFBFBD>
-3. LinkedList <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>λ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ɾ<EFBFBD><EFBFBD>Ԫ<EFBFBD>ظ<EFBFBD><EFBFBD>졣
+1.  ArrayList 基于动态数组实现，LinkedList 基于双向循环链表实现；
+2. ArrayList 支持随机访问，LinkedList 不支持；
+3. LinkedList 在任意位置添加删除元素更快。

-## 2. Vector <EFBFBD><EFBFBD> Stack
+## 2. Vector 与 Stack

 [Vector.java](https://github.com/CyC2018/InterviewNotes/blob/master/notes/src/Vector.java)

@ -242,13 +243,13 @@ private void writeObject(java.io.ObjectOutputStream s)

 [HashMap.java](https://github.com/CyC2018/InterviewNotes/blob/master/notes/src/HashMap.java)

-ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͻ<EFBFBD><EFBFBD>
+使用拉链法来解决冲突。

-Ĭ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> capacity Ϊ 16<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫע<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>뱣֤Ϊ 2 <20>Ĵη<C4B4><CEB7><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> Entry[] table <20><><EFBFBD><EFBFBD><EFBFBD>ĳ<EFBFBD><C4B3>ȣ<EFBFBD>size <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʵ<EFBFBD><CAB5>ʹ<EFBFBD><CAB9><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+默认容量 capacity 为 16，需要注意的是容量必须保证为 2 的次方。容量就是 Entry[] table 数组的长度，size 是数组的实际使用量。

-threshold <EFBFBD>涨<EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD> size <20><><EFBFBD>ٽ<EFBFBD>ֵ<EFBFBD><D6B5>size <20><><EFBFBD><EFBFBD>С<EFBFBD><D0A1> threshold<6C><64><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڵ<EFBFBD><DAB5>ڣ<EFBFBD><DAA3>ͱ<EFBFBD><CDB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݲ<EFBFBD><DDB2><EFBFBD><EFBFBD><EFBFBD>
+threshold 规定了一个 size 的临界值，size 必须小于 threshold，如果大于等于，就必须进行扩容操作。

-threshold = capacity * load_factor<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> load_factor Ϊ table <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ܹ<EFBFBD>ʹ<EFBFBD>õı<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>load_factor <20><><EFBFBD><EFBFBD><EFBFBD>ᵼ<EFBFBD>¾۴صĳ<D8B5><C4B3>֣<EFBFBD><D6A3>Ӷ<EFBFBD>Ӱ<EFBFBD><D3B0><EFBFBD><EFBFBD>ѯ<EFBFBD>Ͳ<EFBFBD><CDB2><EFBFBD><EFBFBD><EFBFBD>Ч<EFBFBD>ʣ<EFBFBD><CAA3><EFBFBD><EFBFBD><EFBFBD><EFBFBD>㷨<EFBFBD>ʼǡ<CABC>
+threshold = capacity * load_factor，其中 load_factor 为 table 数组能够使用的比例，load_factor 过大会导致聚簇的出现，从而影响查询和插入的效率，详见算法笔记。

 ```java
 static final int DEFAULT_INITIAL_CAPACITY = 16;
@ -268,7 +269,7 @@ final float loadFactor;
 transient int modCount;
 ```

-<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ԫ<EFBFBD>ش<EFBFBD><EFBFBD><EFBFBD><EFBFBD>п<EFBFBD><EFBFBD>Կ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> capacity Ϊԭ<CEAA><D4AD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+从下面的添加元素代码中可以看出，当需要扩容时，令 capacity 为原来的两倍。

 ```java
 void addEntry(int hash, K key, V value, int bucketIndex) {
@ -279,7 +280,7 @@ void addEntry(int hash, K key, V value, int bucketIndex) {
 }
 ```

-Entry <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʾһ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ֵ<EFBFBD><EFBFBD>Ԫ<EFBFBD>أ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>е<EFBFBD> next ָ<><D6B8><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>л<EFBFBD>ʱ<EFBFBD><CAB1>ʹ<EFBFBD>á<EFBFBD>
+Entry 用来表示一个键值对元素，其中的 next 指针在序列化时会使用。

 ```java
 static class Entry<K,V> implements Map.Entry<K,V> {
@ -290,7 +291,7 @@ static class Entry<K,V> implements Map.Entry<K,V> {
 }
 ```

-get() <EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫ<EFBFBD>ֳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>key Ϊ null <EFBFBD><EFBFBD> <20><>Ϊ null<6C><6C><EFBFBD><EFBFBD><EFBFBD>п<EFBFBD><D0BF>Կ<EFBFBD><D4BF><EFBFBD> HashMap <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> null <20><>Ϊ<EFBFBD><CEAA><EFBFBD><EFBFBD>
+get() 操作需要分成两种情况，key 为 null 和 不为 null，从中可以看出 HashMap 允许插入 null 作为键。

 ```java
 public V get(Object key) {
@ -306,7 +307,7 @@ public V get(Object key) {
 }
 ```

-put() <EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҳ<EFBFBD><EFBFBD>Ҫ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> key <EFBFBD>Ƿ<EFBFBD>Ϊ null <EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD>Ĵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҫע<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>û<EFBFBD><EFBFBD> key Ϊ null <EFBFBD>ļ<EFBFBD>ֵ<EFBFBD>ԣ<EFBFBD><EFBFBD>²<EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD> key Ϊ null <EFBFBD>ļ<EFBFBD>ֵ<EFBFBD><EFBFBD>ʱĬ<EFBFBD><EFBFBD><EFBFBD>Ƿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 0 λ<>ã<EFBFBD><C3A3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ϊ null <20><><EFBFBD>ܼ<EFBFBD><DCBC><EFBFBD> hash ֵ<><D6B5>Ҳ<EFBFBD><D2B2><EFBFBD>޷<EFBFBD>֪<EFBFBD><D6AA>Ӧ<EFBFBD>÷<EFBFBD><C3B7><EFBFBD><EFBFBD>ĸ<EFBFBD><C4B8><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ϡ<EFBFBD>
+put() 操作也需要根据 key 是否为 null 做不同的处理，需要注意的是如果本来没有 key 为 null 的键值对，新插入一个 key 为 null 的键值对时默认是放在数组的 0 位置，这是因为 null 不能计算 hash 值，也就无法知道应该放在哪个链表上。

 ```java
 public V put(K key, V value) {
@ -354,8 +355,8 @@ private V putForNullKey(V value) {

 [ConcurrentHashMap.java](https://github.com/CyC2018/InterviewNotes/blob/master/notes/src/HashMap.java)

-[ ̽<EFBFBD><EFBFBD> ConcurrentHashMap <EFBFBD>߲<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ե<EFBFBD>ʵ<EFBFBD>ֻ<EFBFBD><EFBFBD><EFBFBD> ](https://www.ibm.com/developerworks/cn/java/java-lo-concurrenthashmap/)
+[ 探索 ConcurrentHashMap 高并发性的实现机制 ](https://www.ibm.com/developerworks/cn/java/java-lo-concurrenthashmap/)

-# <EFBFBD>ο<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+# 参考资料

- Java <EFBFBD><EFBFBD><EFBFBD><EFBFBD>˼<EFBFBD><EFBFBD>
+- Java 编程思想