Java基础知识强化之集合框架笔记66：Map集合面试题之HashMap和Hashtable区别

 1 package cn.itcast_07;
 2 
 3 import java.util.Hashtable;
 4 
 5 /*
 6  * 1:Hashtable和HashMap的区别?
 7  * Hashtable:线程安全，效率低。不允许null键和null值
 8  * HashMap:线程不安全，效率高。允许null键和null值
 9  * 
10  */
11 public class HashtableDemo {
12     public static void main(String[] args) {
13         // HashMap<String, String> hm = new HashMap<String, String>();
14         Hashtable<String, String> hm = new Hashtable<String, String>();
15 
16         hm.put("it001", "hello");
17         // hm.put(null, "world"); //NullPointerException
18         // hm.put("java", null); // NullPointerException
19 
20         System.out.println(hm);
21     }
22 }