HashMap and Hashtable What is the difference?

In JDK 1.8 HashMap and Hashtable main differences are as follows:

• Different thread safety. HashMap thread-safe; Hashtable method is Synchronize of.
• key, value whether to allow null. The key and value are HashMap may be null, key allows only a null; Hashtable both the key and value is not null.
• Different iterators. The HashMap Iterator iterator is fail-fast; also uses the Hashtable enumerator iterator.
• The different hash calculation. HashMap calculated hash value; the Hashtable hashCode method using the key.
• The default initial size and expansion in different ways. HashMap default initial size 16, capacity must be an integer power of two, when the expansion capacity becomes 2 times the original; the Hashtable default initial size 11, when the expansion capacity becomes doubly original 2 1.
• Is there a method contains. HashMap contains no method; comprising the Hashtable contains method similar containsValue.
• Different parent. HashMap inherited from AbstractMap; Hashtable inherited from the Dictionary.

 

In-depth details, you can refer to:

• https://www.cnblogs.com/williamjie/p/9099141.html

 

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