Java之HashMap用法

 1 package test_demo;
 2 
 3 import java.util.HashMap;
 4 import java.util.Iterator;
 5 import java.util.Map;
 6 import java.util.Random;
 7 
 8 /*
 9  * @desc HashMap测试程序
10  */
11 
12 public class HashMapDemo {
13     private static void testHashMapAPIs() {
14         // 初始化随机种子
15         Random r = new Random();
16         // 新建HashMap
17         HashMap map = new HashMap();
18         // 添加操作
19         map.put("one", r.nextInt(10));
20         map.put("two", r.nextInt(10));
21         map.put("three", r.nextInt(10));
22         // 打印出map
23         System.out.println("map:" + map);
24         // 通过Iterator遍历key-value
25         Iterator iter = map.entrySet().iterator();
26         while (iter.hasNext()) {
27             Map.Entry entry = (Map.Entry) iter.next();
28             System.out.println("next :  " + entry.getKey() + ":" + entry.getValue());
29         }
30         // HashMap的键值对个数
31         System.out.println("size:" + map.size());
32         // containsKey(Object key) :是否包含键key
33         System.out.println("contains key two : " + map.containsKey("two"));
34         System.out.println("contains key five : " + map.containsKey("five"));
35         // containsValue(Object value) :是否包含值value
36         System.out.println("contains value 0 : " + map.containsValue(new Integer(0)));
37         // remove(Object key) ： 删除键key对应的键值对
38         map.remove("three");
39         System.out.println("删除three");
40         System.out.println("map:" + map);
41         // clear() ： 清空HashMap
42         map.clear();
43         System.out.println("清空HashMap");
44         // isEmpty() : HashMap是否为空
45         System.out.println((map.isEmpty() ? "map is empty" : "map is not empty"));
46     }
47 
48     public static void main(String[] args) {
49         testHashMapAPIs();
50     }
51 }