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是否可以实现由给定HashSet实现支持的MyHashMap？

[英]Is it possible to implement a MyHashMap backed by a given HashSet implementation?

原文 2014-01-23 07:06:33 2 1 java/ data-structures/ hashmap/ hashset

As we all known, in Sun(Oracle) JDK, HashSet is implemented backed by a HashMap , to reuse the complicated algorithm and data structure. 众所周知，在Sun（Oracle）JDK中， HashSet由HashMap支持，以重用复杂的算法和数据结构。 But, is it possible to implement a MyHashMap using java.util.HashSet as its back? 但是，是否可以使用java.util.HashSet作为其背面实现MyHashMap ？ If possible, how? 如果可能，怎么样？ If not, why? 如果没有，为什么？

Please note that this question is only a discussion of coding skill, not applicable for production scenarios. 请注意，此问题仅是对编码技巧的讨论，不适用于生产场景。

1 个解决方案

Trove bases it's Map on it's Set implementation. Trove将它的Map基于它的Set实现。 However, it has one critical method which is missing from Set which is a get() method. 但是，它有一个缺少Set的关键方法，它是一个get（）方法。

Without a get(Element) method, HashSet you cannot perform a lookup which is a key function of a Map. 如果没有get（Element）方法，HashSet就无法执行查找，这是Map的关键功能。 (pardon the pun) The only option Set has is a contains which could be hacked to perform a get() but it would not be ideal. （原谅双关语）唯一的选择Set是一个包含可以被黑客攻击来执行get（）但它不是理想的。

You can have; 你可以有;

a Set where the Entry is a key and a value. a Entry是键和值的集合。
you define entries as being equal when the keys are the same. 在键相同时将条目定义为相等。
you hack the equals() method so when there is a match, that on a "put" the value portion of an entry is updated, and on a "get" the value portion is copied. 你破解equals（）方法所以当匹配时，在“put”上更新条目的值部分，并在“get”上复制值部分。

Set could have been designed to be extended as Map, but it wasn't and it wouldn't be a good idea to use HashSet or the existing Set implementations to create a Map. Set可以被设计为扩展为Map，但它不是，并且使用HashSet或现有的Set实现来创建Map不是一个好主意。