是否有可能TreeSet等于HashSet但不等于HashSet等于TreeSet [英] Is it possible that TreeSet equals HashSet but not HashSet equals TreeSet

问题描述

我今天进行了一次采访，接受采访的人对他的陈述感到困惑，他问 TreeSet 是否等于 HashSet 而不是 HashSet 等于 TreeSet 。我说不。

I had a interview today and the person taking my interview puzzled me with his statement asking if it possible that TreeSet equals HashSet but not HashSet equals TreeSet. I said "no" but according to him the answer is "yes".

怎么可能？

推荐答案

您的面试官是正确的，他们在某些特定情况下不具有对等关系。 TreeSet 可能等于 HashSet ，反之亦然。下面是一个示例：

Your interviewer is right, they do not hold equivalence relation for some specific cases. It is possible that TreeSet can be equal to HashSet and not vice-versa. Here is an example:

TreeSet<String> treeSet = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
HashSet<String> hashSet = new HashSet<>();
treeSet.addAll(List.of("A", "b"));
hashSet.addAll(List.of("A", "B"));
System.out.println(hashSet.equals(treeSet)); // false
System.out.println(treeSet.equals(hashSet)); // true

原因是 TreeSet 使用比较器确定元素是否重复，而 HashSet 使用 equals 。

The reason for this is that a TreeSet uses comparator to determine if an element is duplicate while HashSet uses equals.

引用 TreeSet ：

请注意顺序由集合维护（无论是否提供显式比较器） 必须与equals 保持一致，才能正确实现Set接口。

Note that the ordering maintained by a set (whether or not an explicit comparator is provided) must be consistent with equals if it is to correctly implement the Set interface.

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