如何从通用 ArrayList 中找到最小值、最大值和平均值 [英] How to find minimum, maximum and average value from a Generic ArrayList

问题描述

我有 3 类宠物、猫和狗类.Cat 和 Dog 类是 Pet 类的子类，我已经覆盖了 toString 方法.我在 Dog 类中重写的 toString 方法打印了 Dog 类的 name 字段和 weight 字段.我创建了一个名为 mainList 的 ArrayList，我需要一个方法来计算 ArrayList 中权重的最小值、最大值和平均值. 你能告诉我如何创建一个计算最小值的方法，ArrayList中Dog对象权重的最大值和平均值?

I have 3 classes Pet, Cat and Dog classes. Cat and Dog classes are childs of Pet class and I've overrided toString method. The toString method that I overrided in Dog class prints the name field and weight field of Dog class. I've created an ArrayList called mainList and I need a method which calculates minimum, maximum and avarage value of weights in ArrayList. Can you tell me how can I create a method that calculates minimum, maximum and avarage values of weights of Dog Objects in ArrayList?

我的课程在下面...

宠物类:

public class Pet
{
    private String name;



    public String getName()
    {
        return name;
    }

    protected void setName(String newName)
    {
        name = newName;
    }

    public Pet(String petName) {
        name = petName;
    }
} 

狗类:

public class Dog extends Pet
{

    private Double weight;

    public double getWeight()
    {
        return weight;
    }

    protected void setWeight(double newWeight)
    {
        weight = newWeight;
    }

    public String toString() {
        return String.format("%s , %f", getName(), getWeight());
    }

    public Dog(String petName, double dogWeight)
    {
        super(petName);
        weight = dogWeight;

    }
}

宠物测试类:

import java.util.*;

public class PetTest
{
    static ArrayList<Pet> mainList = new ArrayList<Pet>();
    static Iterator<Pet> mainIter = mainList.iterator();
    static Scanner keyboard = new Scanner(System.in);

    public static void eighthCase()
    {
      // I need a method here
    }

    public static void listThemAll()
    {
        for(Pet pet: mainList)
        {
            System.out.println(pet.toString());
        }
    }

    public static void listDogs()
    {
            for(Pet pet: mainList)
            {
                if (pet instanceof Dog)
                {
                    System.out.println(pet.toString());
                }
            }//end of for loop
    }//end of listDogs method

    public static void listCats()
    {
            for(Pet pet: mainList)
            {
                if(pet instanceof Cat)
                {
                    System.out.println(pet.toString());
                }
            }//end of for loop

    }//end of listCats method

    public static void addDog(String dogName,Double dogWeight)
    {
        Pet dog = new Dog(dogName, dogWeight);
        mainList.add(dog);
    }//end of addDog method

    public static void addCat(String catName, String furColor)
    {
        Pet cat = new Cat(catName, furColor);
        mainList.add(cat);
    }//end of addCat method

    public static void removeDog(String dogName)
    {
        for(Pet pet : mainList)
            {
                if((pet instanceof Dog) && (pet.getName().equals(dogName)))
                {
                    mainList.remove(pet);
                }//end of if statement
            }//end of for loop

    }//end of removeDog method


    public static void removeCat(String catName)
    {
            for(Pet pet : mainList)
            {
                if((pet instanceof Cat) && (pet.getName().equals(catName)))
                {
                    mainList.remove(pet);

                }//end of if statement

            }//end of for loop

    }//end of removeCat method

    public static void showMenu()
    {
        System.out.println("1. Add dog ");
        System.out.println("2. Add cat");
        System.out.println("3. Remove dog");
        System.out.println("4. Remove cat");
        System.out.println("5. List dogs");
        System.out.println("6. List cats");
        System.out.println("7. List all pets");
        System.out.println("8. Show min, max and average weight of dogs");
        System.out.println("0. Quit");
        int action = keyboard.nextInt();

        Scanner parameter1 = new Scanner(System.in);
        Scanner parameter2 = new Scanner(System.in);

        while(action > 0 && action <= 8)
        {
        switch(action)
        {
        case 1: 
            System.out.println("Type in the name of the dog that you want to add.");
            String dogName = parameter1.next();
            System.out.println("Type in the weight of the dog that you want to add.");
            Double dogWeight = parameter2.nextDouble();
            addDog(dogName,dogWeight);
            showMenu();

            break;

        case 2:
            System.out.println("Type in the name of the cat that you want to add.");
            String catName = parameter1.next();
            System.out.println("Type in the color of the cat that you want to add.");
            String furColor = parameter2.next();
            addCat(catName,furColor);
            showMenu();

            break;

        case 3:
            System.out.println("Type in the name of dog that you want to remove.");
            String dogToRemove = parameter1.next();
            removeDog(dogToRemove);
            showMenu();

            break;

        case 4:
            System.out.println("Type in the name of dog that you want to remove.");
            String catToRemove = parameter1.next();
            removeDog(catToRemove);
            showMenu();

            break;

        case 5:
            listDogs();
            showMenu();

            break;

        case 6:
            listCats();
            showMenu();
            break;

        case 7:
            listThemAll();
            showMenu();
            break;

        case 8:
            eighthCase();
            break;


        }//end of switch statement

        }//end of while loop
    }//end of showMenu method

    public static void main(String[] args)
    {

        showMenu();



        }//end of main method



}//end of the class

推荐答案

我会这样做(底部较短):

I would do it like this (bottom one is shorter):

public static void calculateDogValues(){
    List<Double> dogWeightList = new ArrayList<>();
    double max = 0, min = 0, average = 0;
       for(Pet pet: mainList){
          if (pet instanceof Dog){    //add all dog weights to list
              dogWeightList.add(pet.getWeight());
          }
       }

       Collections.sort(dogWeightList);   //sort the list
       min = dogWeightList.get(0);   //get smallest value
       max = dogWeightList.get(dogWeightList.size()-1);   //get highest value

       for (double weight : dogWeightList) {   //make sum of all weights
          average += weight;
       }
       average = average/dogWeightList.size();   //sum/number of weights

       System.out.println("Minimum weight is " + min);
       System.out.println("Maximum weight is " + max);
       System.out.println("Average weight is " + average);

    }

或者像这样没有排序:

    double max = 0, min = 0, average = 0, amountOfDogs = 0;
       for(Pet dog: mainList){
          if (dog instanceof Dog){   
              min = Math.min(min, dog.getWeight()); 
              max = Math.max(max, dog.getWeight());
              average += dog.getWeight();
              amountOfDogs++;
          }
       }
       average = average/amountOfDogs;

       System.out.println("Minimum weight is " + min);
       System.out.println("Maximum weight is " + max);
       System.out.println("Average weight is " + average);

    }

也让你的宠物类成为这样:

Also make your pet class this:

public class Pet{

    private String name;
    private double weight;

    public String getName()
    {
        return name;
    }

    protected void setName(String newName)
    {
        name = newName;
    }

    public Pet(String petName) {
        name = petName;
    }

    public void setWeight(double newWeight){
    weight = newWeight;
    }

    public double getWeight(){
    return weight;
    }
} 

超类没有权重.

这篇关于如何从通用 ArrayList 中找到最小值、最大值和平均值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！