Hash及HashMap简介

 1 import java.util.HashMap;
 2 import java.util.Iterator;
 3 import java.util.Map;
 4 import java.util.Random;
 5 
 6 public class HashMapTest {
 7 
 8     public static void main(String[] args) {
 9         testHashMapAPIs();
10     }
11 
12     private static void testHashMapAPIs() {
13         // 初始化随机种子
14         Random r = new Random();
15         // 新建HashMap
16         HashMap map = new HashMap();
17         // 添加操作
18         map.put("one", r.nextInt(10));
19         map.put("one", r.nextInt(10));
20         map.put("two", r.nextInt(10));
21         map.put("three", r.nextInt(10));
22 
23         // 打印出map
24         System.out.println("map:" + map);
25 
26         // 通过Iterator遍历key-value
27         Iterator iter = map.entrySet().iterator();
28         while (iter.hasNext()) {
29             Map.Entry entry = (Map.Entry) iter.next();
30             System.out.println("next : " + entry.getKey() + " - " + entry.getValue());
31         }
32 
33         // HashMap的键值对个数
34         System.out.println("size:" + map.size());
35 
36         // containsKey(Object key) :是否包含键key
37         System.out.println("contains key two : " + map.containsKey("two"));
38         System.out.println("contains key five : " + map.containsKey("five"));
39 
40         // containsValue(Object value) :是否包含值value
41         System.out.println("contains value 0 : " + map.containsValue(new Integer(0)));
42 
43         // remove(Object key) ： 删除键key对应的键值对
44         map.remove("three");
45 
46         System.out.println("map:" + map);
47 
48         // clear() ： 清空HashMap
49         map.clear();
50 
51         // isEmpty() : HashMap是否为空
52         System.out.println((map.isEmpty() ? "map is empty" : "map is not empty"));
53     }
54 }