一、概述

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LinkedHashSet 实现了 Set 接口，同时 LinkedHashSet 迭代是有序的。

LinkedHashSet 继承自 HashSet

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1、通过 HashSet 实现 Set 的元素唯一性。
2、在 HashSet 中存在私有构造，通过 LinkedHashMap 来实现集合迭代的有序性 《HashSet 私有构造》

二、代码分析

LinkedHashSet 继承于 HashSet ，有基于 LinkedHashMap 《LinkedHashMap》实现。

通过 LinkedHashMap 来保存所有元素，同时使用 LinkedHashMap 中维护的链表来保证迭代的有序性。
通过 HashSet 来保证元素的唯一性。

2.1、构造函数

  1. /**
  2.      * Constructs a new, empty linked hash set with the specified initial
  3.      * capacity and load factor.
  4.      *
  5.      * @param      initialCapacity the initial capacity of the linked hash set
  6.      * @param      loadFactor      the load factor of the linked hash set
  7.      * @throws     IllegalArgumentException  if the initial capacity is less
  8.      *               than zero, or if the load factor is nonpositive
  9.      */
  10.     public LinkedHashSet(int initialCapacity, float loadFactor) {
  11.         super(initialCapacity, loadFactor, true);
  12.     }
  14.     /**
  15.      * Constructs a new, empty linked hash set with the specified initial
  16.      * capacity and the default load factor (0.75).
  17.      *
  18.      * @param   initialCapacity   the initial capacity of the LinkedHashSet
  19.      * @throws  IllegalArgumentException if the initial capacity is less
  20.      *              than zero
  21.      */
  22.     public LinkedHashSet(int initialCapacity) {
  23.         super(initialCapacity, .75f, true);
  24.     }
  26.     /**
  27.      * Constructs a new, empty linked hash set with the default initial
  28.      * capacity (16) and load factor (0.75).
  29.      */
  30.     public LinkedHashSet() {
  31.         super(16, .75f, true);
  32.     }
  34.     /**
  35.      * Constructs a new linked hash set with the same elements as the
  36.      * specified collection.  The linked hash set is created with an initial
  37.      * capacity sufficient to hold the elements in the specified collection
  38.      * and the default load factor (0.75).
  39.      *
  40.      * @param c  the collection whose elements are to be placed into
  41.      *           this set
  42.      * @throws NullPointerException if the specified collection is null
  43.      */
  44.     public LinkedHashSet(Collection<? extends E> c) {
  45.         super(Math.max(2*c.size(), 11), .75f, true);
  46.         addAll(c);
  47.     }

上述所有的构造函数最终调用的都是 HashSet 中的私有构造，如下
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