如何正确使用枚举进行简单的价格计算(Java)

Question

我正在尝试优化一个代码片段，看起来像这样:

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; }
}

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

到目前为止，我的代码是这样的:

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;
}
}

我得到一个错误，因为这段代码:

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

我正试着往字典里添加元素，但我认为这样做不对。

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使这个解决方案工作，然后再尝试使它更好(因为很可能有更好的方法来做到这一点)。

如何正确地创建我试图使用枚举创建的字典?

Answer 1

你的代码中有很多错误。

在Java中创建列表使用的语法不正确(与JavaScript中的工作方式不同):

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

必须与特定枚举常数相关联的枚举字段不应标记为static。修饰符static表示一个字段在一个类的所有实例之间共享，enums在一天结束时是类。如果您希望字符串order对于各种饮料都是唯一的，那么这一行是不正确的:

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;行不会像您期望的那样工作。它不会分配对象属性，而是将参数order重新分配给自己。您应该使用关键字this来引用对象字段的顺序。

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，请查看本教程

旁注:根据Java命名约定下划线应该仅用于常量的名称(如unum-members,static final字段)，但enum的名称必须使用驼峰式BeerCider，如类和接口的名称。

Answer 2

虽然您没有提到您得到了什么错误，但这是您如何填充Kvarteret2构造函数的方法:

// 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>>(); 
List<DrinkIngredients> list=new ArrayList<DrinkIngredients>(); // define ArrayList outside constructor
public Kvarteret2() {
list.add(DrinkIngredients.GIN);
list.add(DrinkIngredients.TONIC);
list.add(DrinkIngredients.MINT);
Drinks.put("GT", ls);
}