使用 Comparator 的 ConcurrentSkipListSet 不会添加新的唯一值

Question

我想要一组按长度最长 -> 最短排序的并发字符串值。

这是我的代码 (JAVA 8):

private ConcurrentSkipListSet<String> sortedSourceTypeNames = new ConcurrentSkipListSet<>(Comparator.comparing(String::length).reversed());

这是 java 8 文档：

    /**
     * Constructs a new, empty set that orders its elements according to
     * the specified comparator.
     *
     * @param comparator the comparator that will be used to order this set.
     *        If {@code null}, the {@linkplain Comparable natural
     *        ordering} of the elements will be used.
     */
    public ConcurrentSkipListSet(Comparator<? super E> comparator) {
        m = new ConcurrentSkipListMap<E,Object>(comparator);
    }

奇怪的是：

添加新值"some_str" -> 确定
添加新值"some_els" -> 未添加
添加新值"some" -> 确定

调试此现象我看到 ConcurrentSkipListSet 正在拒绝新的唯一字符串，这些字符串的长度与集合中已存在的字符串的长度相同。

我就像 Waaaattt?!?!?

这是任何文档中都未提及的意外行为。

这是 JAVA ConcurrentSkipListSet 实现中的错误吗？还是我做的？

编辑：

感谢大家的快速回复！

我只想指出此行为记录在 JAVA SortedSet 接口中（但不在 ConcurrentSkipListSet 中）：

* <p>Note that the ordering maintained by a sorted set (whether or not an
 * explicit comparator is provided) must be <i>consistent with equals</i> if
 * the sorted set is to correctly implement the <tt>Set</tt> interface.  (See
 * the <tt>Comparable</tt> interface or <tt>Comparator</tt> interface for a
 * precise definition of <i>consistent with equals</i>.)  This is so because
 * the <tt>Set</tt> interface is defined in terms of the <tt>equals</tt>
 * operation, but a sorted set performs all element comparisons using its
 * <tt>compareTo</tt> (or <tt>compare</tt>) method, so two elements that are
 * deemed equal by this method are, from the standpoint of the sorted set,
 * equal.  The behavior of a sorted set <i>is</i> well-defined even if its
 * ordering is inconsistent with equals; it just fails to obey the general
 * contract of the <tt>Set</tt> interface.

Answer 1

您提供的比较器 returns 相同长度的字符串相等，因此忽略重复项。

默认使用ConcurrentSkipListSet就像

Set<String> set = new ConcurrentSkipListSet<>(
        Comparator.comparing(s -> s));

或

Set<String> set = new ConcurrentSkipListSet<>(
        Comparator.naturalOrder());

当您设置比较器时，您替换了默认比较器，如果您的比较器声明两个对象相等，它不会默认返回默认行为。

解决此问题的一种方法是先按长度排序，然后再按相等长度的内容排序。

Set<String> set = new ConcurrentSkipListSet<>(
        Comparator.comparing(String::length).reversed()
        .thenComparing(s -> s));

set.add("aa");
set.add("bb");
set.add("aaa");
set.add("ccc");
System.out.println(set);

打印

[aaa, ccc, aa, bb]

使用 Comparator 的 ConcurrentSkipListSet 不会添加新的唯一值

ConcurrentSkipListSet using Comparator will not add new unique values

java

java.util.concurrent

java-8