HashSet与LinkedHashSet [英] HashSet vs LinkedHashSet

问题描述

他们之间有什么区别？我知道

What is the difference between them? I know that

LinkedHashSet是HashSet的有序版本，
维护所有元素的双向链接列表。在关心迭代顺序时，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允许您按插入顺序遍历元素
。

A LinkedHashSet is an ordered version of HashSet that maintains a doubly-linked List across all elements. Use this class instead of HashSet when you care about the iteration order. When you iterate through a HashSet the order is unpredictable, while a LinkedHashSet lets you iterate through the elements in the order in which they were inserted.

但在LinkedHashSet的源代码中，只有HashSet的调用构造函数。那么双链接列表和插入顺序在哪里？

But in sourcecode of LinkedHashSet there are only calling constructors of HashSet. So where is double-linked List and insertion order?

推荐答案

答案在于哪些构造函数 LinkedHashSet 用于构造基类：

The answer lies in which constructors the LinkedHashSet uses to construct the base class:

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);
}

和 HashSet的一个例子构造函数，如下所示：

And (one example of) a HashSet constructor that takes a boolean argument is described, and looks like this:

/**
 * 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);
}

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