Java之HashMap用法

源码：

 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();
     }
 }

执行结果：

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