Java's Hashtable collection

　　Hashtable collection

　　　  java.util.Hashtable <K, V> collection implements Map <K, V> Interface

　　　 Hashtable: the bottom is a hash table, it is a thread-safe collection, is single-threaded collection , slow

　　　 HashMap: the bottom is a hash table, is a thread safe collection is a collection of multi-threaded, high speed

　　　

　　　 HashMap set (the set of all previous studies): store a null value, null key

　　　 Hashtable collection, a null value is not stored, the key null

　　　 

　　　Hashtable and Vector collection as being more advanced collection (HashMap, ArrayList) replaced after jdk1.2 version of the
　　　Hashtable subclass Properties remains active in the stage of history
　　　Properties collection is a unique combination of flow and IO collection