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：

import java.util.*;

/**
 * the basic usage of hashmap
 * @author SheepCore
 * @date 2020-03-03
 */
public class Main {
    public static void main(String[] args) {
        //Created a hashmap and named it fruitStore
        Map<String, Float> fruitStore = new HashMap<>();

        //add some fruit with the tag <name, price> into fruitStore
        fruitStore.put("Apple", 8.98f);
        fruitStore.put("Dragon Fruit", 5.98f);
        fruitStore.put("Red Grape", 6.98f);
        fruitStore.put("Banana", 4.98f);
        fruitStore.put("Durian", 32.8f);

        //update the price of Apple
        fruitStore.put("Apple", 7.50f);

        //the store sold out all the banana, so remove it from the store
        fruitStore.remove("Banana");
        fruitStore.put("Orange", 4.85f);

        //show all kinds of fruit in the store
        Iterator iter = fruitStore.entrySet().iterator();
        while (iter.hasNext()) {
            Map.Entry entry = (Map.Entry)iter.next();
            String name = (String)entry.getKey();
            float price = (float)entry.getValue();
            System.out.printf("%-15s  %-5.2f
", name, price);
        }

        //count the average price of all fruit in the store
        Iterator iter2 = fruitStore.values().iterator();
        float sum = 0f;
        while (iter2.hasNext()) {
            sum += (float)iter2.next();
        }
        System.out.printf("Average Price:  ¥%.2f
", sum / fruitStore.size());
    }
}