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一入 Java 深似海 -- S02E02 学习笔记

news 来源：原创 2024/5/18 23:29:43

一入 Java 深似海 -- S02E02 学习笔记

Java集合
- 1. 概览
- 2. Java 集合框架总览
- - 集合的优势
  - 基本组成
  - - 第三方集合库
    - java.util.Collection 接口
    - java.util.Map 接口
- 3. Java 集合框架內建实现
- 4. Java 集合框架抽象实现
- 5. 集合框架面试题
- 6. 资源推荐

Java集合

集合框架总览
集合框架内建实现
集合框架抽象实现
集合框架面试题

1. 概览

Java8 Documentation
- Reference - Java SE API Documentation
- Learn the Language - Java Tutorials Learning Paths
  - Building On The Foundation - Collections
    - https://docs.oracle.com/javase/tutorial/collections/intro/index.html
    - https://docs.oracle.com/javase/tutorial/collections/interfaces/index.html
- Reference - Developer Guides
  - lang and util Base Libraries - collections
    - https://docs.oracle.com/javase/8/docs/technotes/guides/collections/overview.html
    - https://docs.oracle.com/javase/8/docs/technotes/guides/collections/reference.html

2. Java 集合框架总览

A collection is an object that represents a group of objects (such as the classic Vector class). A collections framework is a unified architecture for representing and manipulating collections, enabling collections to be manipulated independently of implementation details.

集合的优势

Reduces programming effort by providing data structures and algorithms so you don’t have to write them yourself.
- 减少编程的负担
  - 数据结构
    - 链表、栈，队列，树，…
Increases performance by providing high-performance implementations of data structures and algorithms. Because the various implementations of each interface are interchangeable, programs can be tuned by switching implementations.
- 提高性能
Provides interoperability between unrelated APIs by establishing a common language to pass collections back and forth.
- 提供无关 API 之间的互用性
  - Collction.addAll(Collection c)
  - List.addAll(Collection c)
  - Arrays.asList(T… a)
Reduces the effort required to learn APIs by requiring you to learn multiple ad hoc collection APIs.
- 减少学习 API 的负担
  - 相对于数组而言，集合操作更便捷
  - System.arrayCopy(Object src, Object dest, int destPos, int length)
    - Why is Object ? (answer:因为有多维数组的存在，设计时应考虑更大限度的抽象）
Reduces the effort required to design and implement APIs by not requiring you to produce ad hoc collections APIs.
- 减少设计与实现 API 的负担
  - EnumSet.of
Fosters software reuse by providing a standard interface for collections and algorithms with which to manipulate them.
- 促进软件重用

基本组成

Collection interface 集合接口
- Collection
- Map
Infrastructure 基础设施
General-purpose implementations 通用实现
- ArrayList
- LinkedList
- HashMap
- TreeMap
- HashSet
Abstract implementations 抽象实现
Legacy implementations 遗留实现
Convenience implementations 便利实现
- EnumSet
  - Enum
  - Enumeration
- Set.of(T… t)
- ImmutableCollections
Wrapper implementations 包装实现
Special-purpose implementations 特殊实现
- WeakSoftHashMap
Array Utilities 数组工具类
- Arrays
  - binarySearch
Algorithms 算法
Concurrent implementations 并发实现

第三方集合库

guava
apache commons-collections
- Bag
- BoundedMap
  - 范围默认 Integer.MAX_VALUE

java.util.Collection 接口

通用接口
- java.util.Collection
  - iterator()
    - ConcurrentModificationException
  - T[] toArray()
- java.util.List
  - int size()
    - 最大 Integer.MAX_VALUE
    - 为何不用 long ? 和底层 CPU 架构有关，在 32 位操作系统上，long 类型非线程安全（占用8字节，即64bit），因为32位OS并不能完整存储一个long类型对象，拆分高位和低位存储。
- java.util.Set
  - 并不能保证有序
- java.util.SortedSet
  - 有序的
- java.util.NavigableSet
  - since 1.6
  - 继承自 SortedSet
  - SortedSet tailSet(E fromElement);
- java.util.Queue
  - Doug Lea
  - add(E e)
    - 与 Collection 中的 add 方法语义中发生一些细微的变化，如抛出的异常
  - 只读 Collections.unmodifiableList
- java.util.Deque
  - 继承 Queue
  - 实现类 LinkedList
并发接口
- java.util.concurrent.BlockingQueue since1.5
- java.util.concurrent.BlockingDeque since1.6
- java.util.concurrent.TransferQueue since1.7
  - 推荐
  - LinkedTransferQueue

java.util.Map 接口

通用接口
- java.util.SortedMap
  - Set 的底层使用的是 Map 的实现；
- java.util.NavigableMap since1.6
并发接口
- java.util.concurrent.ConcurrentMap
  - ConcurrentHashMap
- java.util.concurrent.ConcurrentNavigableMap
  - ConcurrentSkipListMap

小插曲：1. hash 和 equal 方法要写好；2. 反射很耗性能；

一致性哈希 Consistent Hash ：

https://en.wikipedia.org/wiki/Consistent_hashing
https://github.com/Jaskey/ConsistentHash
https://www.toptal.com/big-data/consistent-hashing
https://www.acodersjourney.com/system-design-interview-consistent-hashing/
https://www.jianshu.com/p/58fde9b2d0a3
http://www.zsythink.net/archives/1182/

3. Java 集合框架內建实现

遗留实现
- java.util.Vector
  - 与 ArrayList 比较
  - synchronized
- java.util.Stack
  - 继承 Vector
  - LIFO
  - 频繁扩容
- java.util.Hashtable
  - 对比 HashMap
    - synchronized
  - 继承 Dictionary
- java.util.Enumeration
  - vs Enum
  - StringTokenizer
- java.util.BitSet
通用实现
并发接⼝
- java.util.concurrent.BlockingQueue
- java.util.concurrent.TransferQueue
- java.util.concurrent.BlockingDeque
- java.util.concurrent.ConcurrentMap
- java.util.concurrent.ConcurrentNavigableMap
并发实现
- java.util.concurrent.LinkedBlockingQueue
- java.util.concurrent.ArrayBlockingQueue
- java.util.concurrent.PriorityBlockingQueue
- java.util.concurrent.DelayQueue
- java.util.concurrent.SynchronousQueue
- java.util.concurrent.LinkedBlockingDeque
- java.util.concurrent.LinkedTransferQueue
- java.util.concurrent.CopyOnWriteArrayList
- java.util.concurrent.CopyOnWriteArraySet
- java.util.concurrent.ConcurrentSkipListSet
- java.util.concurrent.ConcurrentHashMap
- java.util.concurrent.ConcurrentSkipListMap

4. Java 集合框架抽象实现

基于 java.util.Collection 接⼝
- java.util.AbstractCollection
  - java.util.AbstractList
    - Arrays.ArrayList Arrays.asList(T …)
    - ArrayList
  - java.util.AbstractSet
  - java.util.AbstractQueue(Since Java 1.5)
    - offer peek poll
基于 java.util.Map 接⼝
- java.util.AbstractMap

5. 集合框架面试题

Java Interview Questions.pdf
- 浅拷贝
- 深度拷贝
- 递归拷贝

6. 资源推荐

《Java Generics and Collections》 O’Reilly, October 2006, 0-596-52775-6
Cheat Sheet : https://zeroturnaround.com/rebellabs/Java-Collections-Cheat-Sheet/
- https://www.jrebel.com/blog/java-collections-cheat-sheet