HASHMAP测试

package com.jbx.hash;

import java.util.HashMap;
import java.util.Hashtable;

public class TestHashMap {
	public static void main(String[] args) {
		HashMap<String, String> hashMap = new HashMap<String,String>();
		hashMap.put("null", "hashmap_key为什么可以为空字符串呢？");
		hashMap.put(null, null);
		//是否包含null这个key true
		System.out.println(hashMap.containsKey(null));
		//是否包含null这个value true
		System.out.println(hashMap.containsValue(null));
		
		System.out.println(hashMap.get("null"));
//		System.out.println(hashMap.get(null));
		
	    Hashtable<String,String> hashtable2 = new Hashtable<String,String>();
	    hashtable2.put("null", "hashtable key为什么可以为空字符串呢？");
	    hashtable2.put("hj", "null");
	    System.out.println(hashtable2.containsValue("null"));//true
	    System.out.println(hashtable2.contains("null"));//true
	    System.out.println(hashtable2.containsKey("hj"));//true
	    System.out.println(hashtable2.get("null"));
		System.out.println(hashtable2.get("hj"));
	
	}
}