遍歷map的四種方法

1.獲取Entity集合，使用foreach遍歷

2.獲取key集合，value集合，分別遍歷

3.獲取Entity迭代器進行遍歷

4.獲取key集合，經過get方法獲取value

 

推薦使用第一種，效率高，key和value都有，第四種不推薦，效率較低。

 

SystemTest.java

 1 import java.util.Iterator;
 2 import java.util.Map;
 3 import java.util.Properties;
 4 import java.util.Set;
 5 
 6 /**
 7  * Created by gxf on 2016/12/8.
 8  */
 9 public class SystemTest {
10     public static void main(String args[]){
11         getEnv();
12     }
13 
14     public static void getProperties(){
15         Properties properties = System.getProperties();
16         Iterator iterator = properties.entrySet().iterator();
17         while(iterator.hasNext()){
18             Map.Entry e = (Map.Entry)iterator.next();
19             System.out.println(e.getKey() + "," + e.getValue());
20         }
21     }
22 
23     public static void getEnv(){
24         Map<String, String> mapOfEnv = System.getenv();
25         //first
26         for(Map.Entry<String, String> entry : mapOfEnv.entrySet()){
27             System.out.println(entry.getKey() + ", " + entry.getValue());
28         }
29 
30         //second
31         for(String key : mapOfEnv.keySet()){
32             System.out.println("key = " + key);
33         }
34         for(String value : mapOfEnv.values()){
35             System.out.println("value = " + value);
36         }
37 
38         //third
39         Iterator<Map.Entry<String, String>> iterator = mapOfEnv.entrySet().iterator();
40         while(iterator.hasNext()){
41             Map.Entry<String, String> entry = iterator.next();
42             System.out.println(entry.getKey() + ", " + entry.getValue());
43         }
44 
45         //fourth
46         Set<String> setOfKey = mapOfEnv.keySet();
47         for(String key : setOfKey){
48             System.out.println(key + ", " + mapOfEnv.get(key));
49         }
50     }
51 }