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.
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