使用集合或我的函数计算 ArrayList 中对象的出现次数

Question

我有一个 FlowerClass 对象的 ArrayList。这些 FlowerClass 对象中的每一个都有一个名称。我想通过 ArrayList 并计算它们。我想显示每个的数量。因此，如果我有三个名为 Rose 的 FlowerClass 对象、两个名为 Daffodil 和一个名为 Tulip...我想显示以下内容：

• 找到 3 朵玫瑰
• 找到 3 朵水仙花
• 找到 3 朵郁金香

到目前为止，我已经使用我制作的两个函数正确计算了它。问题是我遍历整个 ArrayList ......所以它会不止一次地向我显示结果。例如，如果用户添加了 3 朵玫瑰和 2 朵水仙花……输出是这样的：

• 找到 3 朵玫瑰
• 找到 3 朵玫瑰
• 找到 3 朵玫瑰
• 找到 2 朵水仙花
• 找到 2 朵水仙花

我知道代码为什么会这样，但我不知道如何删除重复的输出。我也不知道如何正确实现集合。我之前在字符串的 ArrayList 上使用过 Collections ......并且它有效。但是这次我将在对象的 ArrayList 上使用集合，并且我想检查每个特定名称的频率。这是主要的类：

import java.util.Scanner;
import java.util.ArrayList;
import java.util.Collections;

public class MainClass {

    static ArrayList<FlowerClass> flowerPack = new ArrayList<FlowerClass>();


    public static void main(String[] args){
        Scanner input = new Scanner(System.in);

        while(true){
            System.out.println("1. Add flower to flowerpack.");
            System.out.println("2. Remove flower from the flowerpack.");
            System.out.println("3. Search for a flower in the flowerpack."); 
            System.out.println("4. Display the flowers in the flowerpack.");
            System.out.println("5. Exit the program.");

            int userChoice = input.nextInt();

            switch(userChoice){
            case 1:
                addFlower();
                break;
            case 2:
                searchFlower();
                break;
            case 3:
                displayFlowers();
                break;
            case 4:
                    System.out.println("Goodbye!");
                System.exit(0);
            }
        }
    }

    public static void addFlower(){
        if (FlowerClass.numberFlowers() == 25){
            System.out.println("There are 25 flowers in the flowerpack. Remove at least one in order to add more.");
            return;
        }
        Scanner input = new Scanner(System.in);
        System.out.println("What is the flower's name?");
        String desiredName = input.nextLine();
        System.out.println("What is the flower's color?");
        String desiredColor = input.nextLine();
        System.out.println("How many thorns does it have?");
        Scanner input2 = new Scanner(System.in);
        int desiredThorns = input2.nextInt();
        System.out.println("What does it smell like?");
        String desiredSmell = input.nextLine();
        flowerPack.add(new FlowerClass(desiredName, desiredColor, desiredThorns, desiredSmell));
    }

    public static void searchFlower(){
        System.out.println("Enter the flower you want to search for.");
        Scanner input = new Scanner(System.in);
        String userChoice = input.nextLine();
        int occurrences  = 0;

        for (FlowerClass flower: flowerPack){
            String name = flower.getName();
            if (userChoice.equals(name)){
                occurrences++;
            }

            else if(occurrences == 0){
                System.out.println("Match not found.");
                return;
            }
        }

        System.out.println("Found " + occurrences + " " + userChoice);
    }

    public static void searchFlower(String desiredFlower){
        int occurrences = 0;

        String userChoice = desiredFlower;
        for (FlowerClass flower: flowerPack){
            String name = flower.getName();
            if (userChoice.equals(name)){
            occurrences++;
            }
        }

        System.out.println("Found " + occurrences + " " + userChoice);
    }

    public static void displayFlowers(){
        int repeats = 0;

        /*for (FlowerClass flower: flowerPack){
            System.out.println(flower.getName());
        }
        System.out.println("Number of flowers in pack: " + FlowerClass.numberFlowers());*/

            //int occurrences = Collections.frequency(flowerPack, name);
            //System.out.println(name + ": " + occurrences);
        for (FlowerClass flower: flowerPack){
            String name = flower.getName();
            searchFlower(name);
        }
    }
}

这是 FlowerClass：

public class FlowerClass {

    public static int numberOfFlowers = 0;
    public String flowerName = null;
    public String flowerColor = null;
    public int numberThorns = 0;
    public String flowerSmell = null;

    FlowerClass(){

    }

    FlowerClass(String desiredName, String desiredColor, int desiredThorns, String desiredSmell){
        flowerName = desiredName;
            flowerColor = desiredColor;
        numberThorns = desiredThorns;
        flowerSmell = desiredSmell;
        numberOfFlowers++;
    }

    public void setName(String desiredName){
        flowerName = desiredName;

    }

    public String getName(){
        return flowerName;
    }

    public static int numberFlowers(){
        return numberOfFlowers;
    }
}

如果您查看我在主类中的最后一个函数，您会发现我注释掉了我尝试实现 Collections.frequency 的方式。我还尝试制作一个多维字符串数组并存储花的名称以及数组中的花数。这是正确计算所有内容，但我不确定如何在计数旁边显示名称。它变得非常混乱，所以我暂时放弃了这种尝试，转而尝试其他两种选择。如果我能找到一种方法来擦除重复的输出行（或者如果我能找到一种让 Collections 工作的方法），那么我就不需要修补多维数组了。

任何提示将不胜感激。感谢您的时间。

Answer 1

您可以将您的花放在Set 中。但我能想到的最简单的解决方案是对你的花进行分类。所以首先，实现一个Comparator<FlowerClass>

public static class FlowerComparator implements Comparator<FlowerClass> {
  @Override
  public int compare(FlowerClass o1, FlowerClass o2) {
    return o1.getName().compareTo(o2.getName());
  }
}

然后就可以用Collections.sort(List, Comparator)排序了

FlowerComparator flowerComparator = new FlowerComparator();
Collections.sort(flowerPack, flowerComparator);

然后你的for 循环需要是这样的（停止搜索相同的花），

String lastName = null;
for (int i = 0; i < flowerPack.size(); i++){
  FlowerClass flower = flowerPack.get(i);
  String name = flower.getName();
  if (lastName == null || !lastName.equals(name)) {
    lastName = name;
    searchFlower(name); // or return the number found, and then add that count to i.
  }
 }

Answer 2

有趣的代码，但它不像我那样工作。

在当前的情况下，您需要跟踪您已经遇到的花名：

public static void displayFlowers(){
    //int repeats = 0;
    List<String> displayedFlowerTypes = new ArrayList<String>();
    for (FlowerClass flower: flowerPack){
        String name = flower.getName();
        if(!displayedFlowerTypes.contains(name))
        {
            displayedFlowerTypes.add(name);
            searchFlower(name);
        }
    }
}

我宁愿做的是维护一个跟踪花卉类型数量的地图，并从中获取类型的数字：

public class MainClass {

static List<FlowerClass> flowerPack = new ArrayList<FlowerClass>();
static Map<String, Integer> flowerCount = new HashMap<String, Integer>();

public static void addFlower() {
    if (FlowerClass.numberFlowers() == 25) {
        System.out.println("There are 25 flowers in the flowerpack. Remove at least one in order to add more.");
        return;
    }
    Scanner input = new Scanner(System.in);
    System.out.println("What is the flower's name?");
    String desiredName = input.nextLine();
    System.out.println("What is the flower's color?");
    String desiredColor = input.nextLine();
    System.out.println("How many thorns does it have?");
    Scanner input2 = new Scanner(System.in);
    int desiredThorns = input2.nextInt();
    System.out.println("What does it smell like?");
    String desiredSmell = input.nextLine();
    flowerPack.add(new FlowerClass(desiredName, desiredColor, desiredThorns, desiredSmell));
    if(!flowerCount.containsKey(desiredName))
    {
        flowerCount.put(desiredName, 1);
    }
    else
    {
        int currentCount = flowerCount.get(desiredName);
        flowerCount.put(desiredName, currentCount+1));
    }
}

这样，您可以将花朵显示如下：

    public static void displayFlowers() {
        for (String name : flowerCount.keySet()) {
            //searchFlower(name);
            System.out.println("Found " + flowerCount.get(name) + " " + name);
        }
    }