Java之HashMap用法

 package test_demo;

 import java.util.HashMap;

 import java.util.Iterator;

 import java.util.Map;

 import java.util.Random;

 /*

  * @desc HashMap测试程序

  */

 public class HashMapDemo {

     private static void testHashMapAPIs() {

         // 初始化随机种子

         Random r = new Random();

         // 新建HashMap

         HashMap map = new HashMap();

         // 添加操作

         map.put("one", r.nextInt(10));

         map.put("two", r.nextInt(10));

         map.put("three", r.nextInt(10));

         // 打印出map

         System.out.println("map:" + map);

         // 通过Iterator遍历key-value

         Iterator iter = map.entrySet().iterator();

         while (iter.hasNext()) {

             Map.Entry entry = (Map.Entry) iter.next();

             System.out.println("next :  " + entry.getKey() + ":" + entry.getValue());

         }

         // HashMap的键值对个数

         System.out.println("size:" + map.size());

         // containsKey(Object key) :是否包含键key

         System.out.println("contains key two : " + map.containsKey("two"));

         System.out.println("contains key five : " + map.containsKey("five"));

         // containsValue(Object value) :是否包含值value

         System.out.println("contains value 0 : " + map.containsValue(new Integer(0)));

         // remove(Object key) ： 删除键key对应的键值对

         map.remove("three");

         System.out.println("删除three");

         System.out.println("map:" + map);

         // clear() ： 清空HashMap

         map.clear();

         System.out.println("清空HashMap");

         // isEmpty() : HashMap是否为空

         System.out.println((map.isEmpty() ? "map is empty" : "map is not empty"));

     }

     public static void main(String[] args) {

         testHashMapAPIs();

     }

 }

map:{one=1, two=9, three=2}

next :  one:1

next :  two:9

next :  three:2

size:3

contains key two : true

contains key five : false

contains value 0 : false

删除three

map:{one=1, two=9}

清空HashMap

map is empty