计算咖啡价格的枚举浮点数问题

Question

package Main;

import java.util.ArrayList;
import java.util.List;

public class Main {
    List<Ingredients> ingredients = new ArrayList<>();
    
    public enum Ingredients { 
        SUGAR(0.25), // these are the problem
        MILK(1.25), // this
        CREAM(1.75); // and this one
        
        private final float cost;

        Ingredients(int cost) {
            this.cost = cost;
        }

        public float getCost() {
            return cost;
        }
    }

    public enum Sizes {
        SMALL(5),
        MEDIUM(10),
        LARGE(15);
        
        private final int cost;

        Sizes(int cost) {
            this.cost = cost;
        }

        public int getCost() {
            return cost;
        }
    }

    public static float calculateCost(Sizes size, List<Ingredients> ingredients) {
        int totalCost = size.getCost();
        for (Ingredients ingredient : ingredients) {
            totalCost += ingredient.getCost();
        }
        return totalCost;
    }

    public static void main(String[] args) {
        List<Ingredients> ingredients = new ArrayList<>();
        ingredients.add(Ingredients.MILK);
        ingredients.add(Ingredients.SUGAR);
        System.out.println("Cost of a small size coffee with milk and suger: " + calculateCost(Sizes.SMALL, ingredients));
    }

我期待一个带有数字的浮点数

6.5

这是输出

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Main.Main$Ingredients.getCost()" because "ingredient" is null
    at Java/Main.Main.calculateCost(Main.java:44)
    at Java/Main.Main.main(Main.java:53)

它说这是一个问题

totalCost += ingredient.getCost();

但这并不是问题，直到我将枚举成分设为浮点数

我对 Java 编码相当陌生，所以我对枚举不太了解，所以我稍后可能会了解更多关于它们的信息

Answer 1

以下是更正后的类型。

public class CoffeOrder {

   
        List<Ingredients> ingredients = new ArrayList<>();
        
        public enum Ingredients { 
            SUGAR(0.25), // these are the problem
            MILK(1.25), // this
            CREAM(1.75); // and this one
            
            private final double cost;

            Ingredients(double cost) {
                this.cost = cost;
            }

            public double getCost() {
                return cost;
            }
        }

        public enum Sizes {
            SMALL(5),
            MEDIUM(10),
            LARGE(15);
            
            private final int cost;

            Sizes(double cost) {
                this.cost = cost;
            }

            public double getCost() {
                return cost;
            }
        }

        public static double calculateCost(Sizes size, List<Ingredients> ingredients) {
            double totalCost = size.getCost();
            for (Ingredients ingredient : ingredients) {
                totalCost += ingredient.getCost();
            }
            return totalCost;
        }

        public static void main(String[] args) {
            List<Ingredients> ingredients = new ArrayList<>();
            ingredients.add(Ingredients.MILK);
            ingredients.add(Ingredients.SUGAR);
            System.out.println("Cost of a small size coffee with milk and suger: " + calculateCost(Sizes.SMALL, ingredients));
        }

}

打印

Cost of a small size coffee with milk and suger: 6.5