Java学习-HashMap性能简单测试

 1 package Collection;
 2 
 3 import java.util.ArrayList;
 4 import java.util.HashMap;
 5 
 6 import charactor.Hero;
 7 
 8 public class HashTest {
 9 
10     public static void main(String[] args) {
11         ArrayList<Hero> heros = new ArrayList<Hero>();
12         HashMap<String, ArrayList<Hero>> hashHeros = new HashMap<>();        //key：String便于直接定位"hero-5555"，value：ArrayList<Hero>记录key值重复的英雄
13         int n = 3000000;
14 
15         for (int i = 0; i < n; i++) {
16             Hero h = new Hero("hero-" + (Math.round(Math.random() * 9000) + 1000));
17             heros.add(h);
18             
19             ArrayList <Hero>tmpArr=new ArrayList<>();    
20             tmpArr.add(h);            
21             if(hashHeros.get(h.name) != null){    //key值若重复，不加入hashMap,但是在其key对应的value    里(tmpArr<Hero>)记录下这个英雄
22                 hashHeros.get(h.name).add(h);
23             }else{
24                 hashHeros.put(h.name, tmpArr);
25             }
26         }
27         // System.out.println(heros);
28         long st1 = System.currentTimeMillis();
29         int cnt1 = 0;    //记录for循环找到的hero-5555的英雄个数
30         for (int i = 0; i < n; i++) {
31             if (heros.get(i).name.equals("hero-5555")) {
32                 cnt1++;
33             }
34 
35         }
36         long et1 = System.currentTimeMillis();
37         System.out.println("for循环共耗时：" + (et1 - st1) + " ms");
38         System.out.println("一共找到" + cnt1 + "个");
39 
40         long st2 = System.currentTimeMillis();
41         ArrayList<Hero> tmpArr=hashHeros.get("hero-5555");        
42         long et2 = System.currentTimeMillis();
43         
44         System.out.println("hashMap共耗时：" + (et2 - st2) + " ms");
45         System.out.println("一共找到" + tmpArr.size() + "个");
46 
47     }
48 }