hashmap笔记

hashmap用法笔记

View Code

 1 package com.app;
 2 
 3 import java.util.HashMap;
 4 import java.util.Iterator;
 5 
 6 public class app {
 7 
 8     /**
 9      * @param args
10 */
11     public static void main(String[] args) {
12         // TODO Auto-generated method stub    
13         HashMap<String, Double> map = new HashMap<String, Double> ();
14         
15         map.put("hello", 1.0);
16         map.put("fine", 2.0);
17         map.put("suck", 3.0);
18         
19         Iterator<String>  it = map.keySet().iterator();
20         
21         if(map.containsKey("why")){
22             System.out.println("Key why exist");
23         }
24         
25         if(map.containsValue(2.0)){
26             System.out.println("Value 2 exist");
27         }
28         
29         /***Hash的遍历***/
30         if(!map.isEmpty()){
31             while(it.hasNext()){
32                 String tempKey = it.next();
33                 if(tempKey.equals("fine")){
34                     Double tempValue = map.get(tempKey) + 10;
35                     map.put(tempKey, tempValue);
36                     
37                     System.out.println("fine is update to " + tempValue);
38                 }else{
39                     System.out.println(map.get(tempKey));
40                 }            
41             }
42         }else{
43             System.out.println("map is empty");
44         }
45         
46         map.clear();
47         
48         if(map.isEmpty()){
49             System.out.println("map is empty");
50         }
51     }
52 }

hashmap的排序：

View Code

 1 package com.app;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Collections;
 5 import java.util.Comparator;
 6 import java.util.HashMap;
 7 import java.util.List;
 8 import java.util.Map;
 9 
10 public class app {
11 
12     /**
13      * @param args
14 */
15     public static void main(String[] args) {
16         // TODO Auto-generated method stub
17         Map<String, Integer> map = new HashMap<String, Integer>();
18         map.put("hello", 1);
19         map.put("fine", 3);
20         map.put("abandon", 2);
21         
22         List<Map.Entry<String, Integer>> list = 
23             new ArrayList<Map.Entry<String, Integer>>(map.entrySet());
24         
25         for(int i = 0; i < list.size(); i++){
26             String id = list.get(i).getKey();
27             System.out.println(id);
28         }
29         
30         Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
31             public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2){
32                 return (o1.getKey()).toString().compareTo(o2.getKey());
33             }//String类的compareTo方法实现字典排序
34         });
35         
36         for(int i = 0; i < list.size(); i++){
37             String id = list.get(i).getKey();
38             System.out.println(id);
39         }    
40     }
41 }