HashTable

public class Hashtable<K,V>
    extends Dictionary<K,V>
    implements Map<K,V>, Cloneable, java.io.Serializable {
	
}

HashTable继承于Dictionary类，字典类是一个抽象类，而且已经被废弃了

//NOTE: This class is obsolete.  New implementations should
//implement the Map interface, rather than extending this class.

对于Hashtable使用场景也很少，因为JDK中有一个和他类似的类，HashMap。

Hashtable和Hashmap的区别：

(The {@code HashMap}class is roughly equivalent to {@code Hashtable}, except that it is unsynchronized and permits nulls.) 

HashTable比HashMap多了同步，少了对null的支持，，所以我们可以直接移步到HashMap。