Java学习-HashMap练习

 1 package Collection;
 2 
 3 import java.util.ArrayList;
 4 import java.util.HashMap;
 5 import java.util.List;
 6 
 7 public class test7 {
 8 
 9     public static void main(String[] args) {
10         HashMap<String, String> hm = new HashMap<>();
11         hm.put("adc", "物理英雄");
12         hm.put("apc", "魔法英雄");
13         hm.put("t", "坦克");
14         System.out.println(hm);
15         // hm.keySet()和hm.values()都是返回Collection，Collection不能直接转换成List，解决办法是直接构造ArrayList
16         // 解决办法二：Collection先转数组：toArray()，再转List：Arrays.asList();
17         // List<Object> testList= Arrays.asList(hm.keySet().toArray());
18         List<String> keysList = new ArrayList<String>(hm.keySet());
19         List<String> valuesList = new ArrayList<String>(hm.values());
20 
21         hm.clear();
22         for (int i = 0; i < keysList.size(); i++) {
23             hm.put(valuesList.get(i), keysList.get(i));
24         }
25         System.out.println(hm);
26 
27     }
28 }