HashSet与LinkedHashSet

Question

它们之间有什么区别？我知道

LinkedHashSet是HashSet的有序版本，可在所有元素上维护双链列表。当您关心迭代顺序时，请使用此类而不是HashSet。当您遍历HashSet时，顺序是不可预测的，而LinkedHashSet可让您按插入元素的顺序来遍历元素。

但是在LinkedHashSet的源代码中，只有HashSet的调用构造函数。那么双向链接的列表和插入顺序在哪里？

Answer 1

答案就在 其中构造 的LinkedHashSet用途，构建基类：

public LinkedHashSet(int initialCapacity, float loadFactor) {
    super(initialCapacity, loadFactor, true);      // <-- boolean dummy argument
}

...

public LinkedHashSet(int initialCapacity) {
    super(initialCapacity, .75f, true);            // <-- boolean dummy argument
}

...

public LinkedHashSet() {
    super(16, .75f, true);                         // <-- boolean dummy argument
}

...

public LinkedHashSet(Collection<? extends E> c) {
    super(Math.max(2*c.size(), 11), .75f, true);   // <-- boolean dummy argument
    addAll(c);
}

并且HashSet描述了一个采用布尔参数的构造函数（的一个示例），看起来像这样：

/**
 * Constructs a new, empty linked hash set.  (This package private
 * constructor is only used by LinkedHashSet.) The backing
 * HashMap instance is a LinkedHashMap with the specified initial
 * capacity and the specified load factor.
 *
 * @param      initialCapacity   the initial capacity of the hash map
 * @param      loadFactor        the load factor of the hash map
 * @param      dummy             ignored (distinguishes this
 *             constructor from other int, float constructor.)
 * @throws     IllegalArgumentException if the initial capacity is less
 *             than zero, or if the load factor is nonpositive
 */
HashSet(int initialCapacity, float loadFactor, boolean dummy) {
    map = new LinkedHashMap<E,Object>(initialCapacity, loadFactor);
}