遍历HashMap的几种方式

Posted 2021-01-04 chenkaixin12121

 1 package com.test;
 2 
 3 import java.util.HashMap;
 4 import java.util.Iterator;
 5 import java.util.Map;
 6 
 7 public class Test {
 8     
 9     public static void main(String[] args) throws Exception {
10 
11         Map<String,String> map = new HashMap<String,String>();
12         map.put("a","a1");
13         map.put("a","a2");
14         map.put("b","b1");
15         map.put("c","c1");
16         
17         System.out.println("-----获得全部key-----");
18         System.out.println(map.keySet());
19         System.out.println("-----获得全部value-----");
20         System.out.println(map.values());
21         
22         System.out.println("-----keySet-----");
23         for(String key : map.keySet()) {
24              System.out.println(key + ":" + map.get(key));
25         }
26         
27         System.out.println("-----entrySet-----");
28         for(Map.Entry<String, String> entry : map.entrySet()) {
29             System.out.println(entry.getKey() + ":" + entry.getValue());
30         }
31         
32         System.out.println("-----iterator-----");
33         //使用iterator遍历 好处是可以删除元素 使用foreach时删除元素则会报错
34         Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
35         while(it.hasNext()) {
36             Map.Entry<String, String> entry = it.next();
37             System.out.println(entry.getKey() + ":" + entry.getValue());
38             //it.remove(); //删除元素
39         }
40         System.out.println("-----Lambda-----");
41         map.forEach((key, value) -> {
42              System.out.println(key + ":" + value);
43         });
44     }
45 }