我的任务是对类别列表进行排序。购物清单，如果你愿意的话。这些类别是来自用户的输入，要购买的物品。在输入所讨论的类别的字符串名称（当然使用扫描仪）之后，用户然后能够输入该类别的数量（整数），然后是该类别的单位成本（双精度）。 系统会提示他们重复此操作，直到他们命名的类别为“结束”。
这一切都很好，花花公子，我已经编写了代码，可以获取所有这些信息，并找到并打印出最大的成本项目，最大数量的项目和其他信息。我需要帮助的是我的重复类别。例如，假设用户输入“cars”后跟一个整数3，后跟数字24000.00。然后他们输入“refigerators”，然后是1，然后是1300.00。然后用户输入第一个条目的副本，即“cars”后跟一个整数5，然后是double 37000.00。如何让我的代码重新访问旧条目，将新数量添加到旧条目，并存储该值而不覆盖旧的东西？我还需要找到列表中项目的最大平均成本。我是HashMap的新手，所以我在努力学习代码：//创建一个arrayList来存储值
// create an arrayList to store values
ArrayList<String> listOne = new ArrayList<String>();
listOne.add("+ 1 item");
listOne.add("+ 1 item");
listOne.add("+ 1 item");
// create list two and store values
ArrayList<String> listTwo = new ArrayList<String>();
listTwo.add("+1 item");
listTwo.add("+1 item");
// put values into map
multiMap.put("some sort of user input detailing the name of the item", listOne);
multiMap.put("some other input detailing the name of the next item", listTwo);
// i need the user to input items until they type "end"
// Get a set of the entries
Set<Entry<String, ArrayList<String>>> setMap = multiMap.entrySet();
// time for an iterator
Iterator<Entry<String, ArrayList<String>>> iteratorMap = setMap.iterator();
System.out.println("\nHashMap with Multiple Values");
// display all the elements
while(iteratorMap.hasNext()) {
Map.Entry<String, ArrayList<String>> entry =
(Map.Entry<String, ArrayList<String>>) iteratorMap.next();
String key = entry.getKey();
List<String> values = entry.getValue();
System.out.println("Key = '" + key + "' has values: " + values);
}
// all that up there gives me this:
具有多个值的HashMap Key ='详细说明下一个项目名称的其他一些输入'具有值：[+ 1项目，+ 1项目] Key ='详细说明项目名称的某种用户输入'具有值：[+ 1项，+ 1项，+ 1项]
但我没有让用户有机会输入物品数量或成本......我迷路了。
答案 0 :(得分：0)
创建一个名为Item的类，而不是操纵三个单独的值。实现Comparable接口，如果它们共享一个公用名，则两个Items相等。有关定义界面的说明，请参阅Javadoc for Comparable。
public class Item implements Comparable {
[...]
}
创建项目列表。
List<Item> shoppingList;
如果要将项目添加到列表中，请先检查列表是否已包含该项目。
// If it's already in the list, add their quantities together
if (shoppingList.contains(newItem))
shoppingList.get(newItem).quantity += newItem.quantity
// Otherwise, add it to the list
else
shoppingList.add(newItem);
答案 1 :(得分：0)
尝试这一小段示例代码，它包含一个Main类和两个依赖类，StatsPrinter和ShoppingEntry
package com.company;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class Main {
public static void main(String[] args) throws IOException {
String category;
String quantity;
String value;
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
HashMap<String, List<ShoppingEntry>> shoppingList = new HashMap<String, List<ShoppingEntry>>();
while(true) {
System.out.print("Enter the category of your item: ");
category = bufferedReader.readLine();
if("end".equals(category)){
break;
}
System.out.print("Enter the quantity of your item: ");
quantity = bufferedReader.readLine();
System.out.print("Enter the value of your item: ");
value = bufferedReader.readLine();
if (shoppingList.containsKey(category)) {
shoppingList.get(category).add(new ShoppingEntry(Integer.parseInt(quantity), Double.parseDouble(value)));
}else{
shoppingList.put(category, new ArrayList<ShoppingEntry>());
shoppingList.get(category).add(new ShoppingEntry(Integer.parseInt(quantity), Double.parseDouble(value)));
}
}
StatsPrinter.printStatistics(shoppingList);
}
}
和ShoppingEntry类
package com.company;
public class ShoppingEntry {
private int quantity;
private double price;
public ShoppingEntry(){
quantity = 0;
price = 0;
}
public ShoppingEntry(int quantity, double price){
this.quantity = quantity;
this.price = price;
}
public int getQuantity() {
return quantity;
}
public void setQuantity(int quantity) {
this.quantity = quantity;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
}
最后是StatsPrinter类，它利用ShoppingEntry的HashMap的数据结构来打印所需的统计数据
package com.company;
import java.text.DecimalFormat;
import java.util.HashMap;
import java.util.List;
public class StatsPrinter {
private static DecimalFormat format = new DecimalFormat("#.##");
public static void printStatistics(HashMap<String, List<ShoppingEntry>> shoppingList) {
printNuumberOfItems(shoppingList);
printLargestValue(shoppingList);
printLargestAverage(shoppingList);
}
private static void printNuumberOfItems(HashMap<String, List<ShoppingEntry>> shoppingList) {
System.out.println("There are " + shoppingList.keySet().size() + " items in your Shopping List");
}
private static void printLargestValue(HashMap<String, List<ShoppingEntry>> shoppingList) {
double currentLargestPrice = 0;
String largestPriceCategory = new String();
for(String keyValue : shoppingList.keySet()) {
for(ShoppingEntry entry : shoppingList.get(keyValue)) {
if (entry.getPrice() > currentLargestPrice) {
currentLargestPrice = entry.getPrice();
largestPriceCategory = keyValue;
}
}
}
System.out.println(largestPriceCategory + " has the largest value of: " + format.format(currentLargestPrice));
}
private static void printLargestAverage(HashMap<String, List<ShoppingEntry>> shoppingList) {
double currentLargestAverage = 0;
String largestAverageCategory = new String();
double totalCost = 0;
int numberOfItems = 0;
for(String keyValue : shoppingList.keySet()) {
for(ShoppingEntry entry : shoppingList.get(keyValue)) {
totalCost += entry.getPrice();
numberOfItems += entry.getQuantity();
}
if((totalCost / numberOfItems) > currentLargestAverage) {
currentLargestAverage = totalCost / numberOfItems;
largestAverageCategory = keyValue;
}
}
System.out.println(largestAverageCategory + " has the largest average value of: " + format.format(currentLargestAverage));
}
}