java - 如何正确使用枚举进行简单的价格计算 (Java)

Question

我正在尝试优化如下所示的代码片段:

public class Kvarteret {
    public static final String ONE_BEER = "hansa";
    public static final String ONE_CIDER = "grans";
    public static final String REAL_BEER = "vestkyst";
    public static final String GT = "gt";
    public static final String BACARDI_SPECIAL = "bacardi_special";

    public int calculatePrice(String drink, boolean student, int amount) {

        if (amount > 2 && (drink == GT || drink == BACARDI_SPECIAL)) {
            throw new RuntimeException("Too many drinks, max 2.");
        }

        int price;

        if (drink.equals(ONE_BEER)) { price = 74;}
        else if (drink.equals(ONE_CIDER)) { price = 103;}
        else if (drink.equals(REAL_BEER)) { price = 110; }
        else if (drink.equals(GT)) { price = ingredient6() + ingredient5() + ingredient4();}
        else if (drink.equals(BACARDI_SPECIAL)) {
            price = ingredient6()/2 + ingredient1() + ingredient2() + ingredient3();
        } else { throw new RuntimeException("Item not in menu"); }

        if (student && (drink == ONE_BEER || drink == ONE_CIDER || drink == REAL_BEER)) { price = price - price/10;}
        return price*amount;
    }

    //rom unit
    private int ingredient1() { return 65;}

    // grenadine unit
    private int ingredient2() { return 10;}

    //lime-juice unit
    private int ingredient3() { return 10;}

    //mint-leafs unit
    private int ingredient4() { return 10; }

    //tonic-water unit
    private int ingredient5() { return 20; }

    //gin unit
    private int ingredient6() { return 85; }
}

该代码是一个计算饮料价格的简单程序。我用了this代码作为起点，因为看起来我们正在尝试做类似的事情。

到目前为止，我的代码如下所示:

import java.util.*;

public class Kvarteret2 {
    private static double price;
    private static double order;

    // Enums defines common values
    private enum Beer_Cider {
        BEER("Hansa", 74), CIDER("Grans", 103), REAL_BEER("Vestkyst", 110);

        private static String order;

        Beer_Cider(String order, double cost) {
            order = order;
            price = cost;
        }

        private static String getOrder() {return order;}
        private static double getCost() {return price;}
    }

    private enum DrinkIngredients {

        ROM("Rom", 65), GRENADINE("Grenadine", 10), LIME("Lime-juice", 10),
        MINT("Mint", 10), TONIC("Tonic-water", 20), GIN("Gin", 85);

        private static String ingredient;

        DrinkIngredients(String ingredient, double cost){
            ingredient = ingredient;
            price = cost;
        }

        private static String getIngredient() {return ingredient;}
        private static double getCost() {return price;}
    }

    // Dictionary with the drink as Key and a list of the ingredients and prices as value
    Map<String, List<DrinkIngredients>> Drinks = new HashMap<String, List<DrinkIngredients>>(); 

    public Kvarteret2() {
        Drinks.put("GT", [DrinkIngredients.GIN, DrinkIngredients.TONIC, DrinkIngredients.MINT]);

    }


    private static double calculate_price(String drink, boolean student, int amount){

        if (amount > 2) {
            throw new IllegalArgumentException("Too many drinks! You can order max 2 drinks at a time.");
        }

        double student_discount = 0.1;

        if (student){
            if (drink == "BEER" || drink == "CIDER" || drink == "REAL BEER") {
                price = amount * (price - price * student_discount);
            }
        }
        return price;
    }
}

由于这段代码，我收到一个错误:

public Kvarteret2() {
    Drinks.put("GT", [DrinkIngredients.GIN, DrinkIngredients.TONIC, DrinkIngredients.MINT]);

}

我正在尝试向字典中添加元素，但我认为这不是正确的做法。

我知道我的代码可能还没有 100% 优化，但我只是想看看我是否可以让这个解决方案工作，然后再尝试让它变得更好(因为很可能有更好的方法来做到这一点)。

如何正确创建我尝试使用枚举创建的字典？

Answer 1

你的代码中有很多错误。

您在 Java 中使用了错误的语法来创建列表(它的工作方式与在 JavaScript 中不同):

[DrinkIngredients.GIN, DrinkIngredients.TONIC, DrinkIngredients.MINT] // <- that's not correct

List.of(DrinkIngredients.GIN, DrinkIngredients.TONIC, DrinkIngredients.MINT) // <- correct

必须与特定枚举常量关联的枚举字段不应标记为static。修饰符 static 表示一个字段在类的所有实例之间共享，一天结束时的 enum 是类。如果您希望字符串 order 对于所有种类的饮料都是唯一的，则此行不正确:

private static String order;

构造函数中的另一个错误:

Beer_Cider(String order, double cost) {
    order = order;
    price = cost;
}

order = order; 行将不会像您预期的那样工作。它不会分配对象属性，而只是将参数 order 重新分配给自己。您应该使用关键字 this引用对象字段顺序。

private enum BeerCider {
    BEER("Hansa", 74), CIDER("Grans", 103), REAL_BEER("Vestkyst", 110);
    
    private String order;
    private double cost;
    
    Beer_Cider(String order, double cost) {
        this.order = order;
        this.cost = cost;
    }
    
    private String getOrder() {return order;}
    private double getCost() {return cost;}
}

有关枚举的更多信息，请查看 this tutorial

旁注: 根据 Java naming conventions下划线只能用于常量的名称(如 unum-members、static final 字段)，但 enum 的名称必须使用驼峰式 BeerCider，如类名和接口(interface)名。