使用Collections或我的函数计算ArrayList中对象的出现

Question

我有一个FlowerClass对象的ArrayList。 每个FlowerClass对象都有一个名称。 我想遍历ArrayList并对其进行计数。 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的对象和一个名为Tulip的对象，我想显示以下内容：

• 找到3朵玫瑰
• 找到3个水仙花
• 找到3郁金香

到目前为止，我已经使用我制作的两个函数对它进行了正确计数。 问题是我遍历了整个ArrayList ...因此它将多次显示结果。 例如，如果用户添加了3朵玫瑰和2个黄水仙...输出如下所示：

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

我知道为什么代码会这样做，但是我不知道如何清除输出的重复。 我也不知道如何正确实现Collections。 在...之前，我已经在字符串的ArrayList上使用过Collections，并且它可以正常工作。 但是这一次，我将在对象的ArrayList上使用Collections，我想检查每个特定名称的出现频率。 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，您会发现我已注释掉尝试实现Collections.frequency的方式。 我还尝试制作一个字符串的多维数组，并存储花朵的名称以及数组中花朵的数量。 这样可以正确计数所有内容，但是我不确定如何在计数旁边显示名称。 事情变得非常混乱，所以我暂时放弃了这一尝试，转而尝试另外两个选项。 如果我可以找到一种方法来消除重复的输出行（或者可以找到一种方法来使Collections正常工作），那么就不需要修改多维数组了。

任何提示将不胜感激。 感谢您的时间。

Answer 1

您可以将您的Flower放在Set 。 但是我能想到的最简单的解决方案是对花朵进行排序。 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，您可以使用Collections.sort(List, Comparator)排序

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

然后您的for循环必须是这样的（停止搜索同一朵花），

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，但是它不能像我那样做。

在当前情况下，您需要跟踪已经遇到的花朵名称：

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Map，该Map跟踪花朵类型的数量，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);
        }
    }