在任何情况下，哈希表都比并发哈希表更好？

Question

众所周知，ConcurrentHashMap在性能上更好，但是我们可以在任何情况下使用Hashtable更好吗？

Answer 1

I'll say this before answering the question: do not ever use Hashtable anymore . Hashtable is a legacy tool from Java 1.0, before the superior collections framework introduced with Java 2 going onwards.

If you require a simple hash map, use HashMap . If you require performing thread-safety, use ConcurrentHashMap . If you require plain basic and non-performing thread-safety, wrap a HashMap into Collections.synchronizedMap(Map) .

Now to actually answer the question as is, which is purely compare two specific classes without seeing the spectrum of possibilities:

Yes, such scenarios exist

From the Hashtable documentation :

If a thread-safe implementation is not needed, it is recommended to use HashMap in place of Hashtable. If a thread-safe highly-concurrent implementation is desired, then it is recommended to use ConcurrentHashMap in place of Hashtable.

1. So yes, Hashtable is appropriate for scenarios where you need a thread-safe implementation, but do not "desire" a highly-concurrent implementation. This, again strictly in the exclusive comparison between ConcurrentHashMap and Hashtable .

2. Also, if you need Enumeration ^[1] , Hashtable has a direct support, while you have to go through Collections.enumeration(...) for other Map s.

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^{1. Enumeration is also a Java 1.0 class. Switch to Iterator (if using Java 2 to 7) or Stream (if using Java 8+)}