Java HashMap 学习笔记

1. 一个简单例子介绍关于Java HashMap 的基本操作：创建、添加、更新、删除及遍历。

2. 代码：

 1 import java.util.*;
 2 
 3 /**
 4  * the basic usage of hashmap
 5  * @author SheepCore
 6  * @date 2020-03-03
 7  */
 8 public class Main {
 9     public static void main(String[] args) {
10         //Created a hashmap and named it fruitStore
11         Map<String, Float> fruitStore = new HashMap<>();
12 
13         //add some fruit with the tag <name, price> into fruitStore
14         fruitStore.put("Apple", 8.98f);
15         fruitStore.put("Dragon Fruit", 5.98f);
16         fruitStore.put("Red Grape", 6.98f);
17         fruitStore.put("Banana", 4.98f);
18         fruitStore.put("Durian", 32.8f);
19 
20         //update the price of Apple
21         fruitStore.put("Apple", 7.50f);
22 
23         //the store sold out all the banana, so remove it from the store
24         fruitStore.remove("Banana");
25         fruitStore.put("Orange", 4.85f);
26 
27         //show all kinds of fruit in the store
28         Iterator iter = fruitStore.entrySet().iterator();
29         while (iter.hasNext()) {
30             Map.Entry entry = (Map.Entry)iter.next();
31             String name = (String)entry.getKey();
32             float price = (float)entry.getValue();
33             System.out.printf("%-15s  %-5.2f\n", name, price);
34         }
35 
36         //count the average price of all fruit in the store
37         Iterator iter2 = fruitStore.values().iterator();
38         float sum = 0f;
39         while (iter2.hasNext()) {
40             sum += (float)iter2.next();
41         }
42         System.out.printf("Average Price:  ¥%.2f\n", sum / fruitStore.size());
43     }
44 }

 

posted @ 2020-03-05 17:49  SheepCore  阅读(171)  评论(0)    收藏  举报