如果查找键是一个String，则为EnumMap或HashMap [英] EnumMap or HashMap if lookup key is a String

问题描述

我试图权衡使用 EnumMap 而不是 HashMap 的优缺点。因为，我总是使用 String 查找，似乎一个 HashMap 与 String 键将是正确的选择。然而， EnumMap 似乎更好的设计，因为它传达我的意图来限制键到一个特定的枚举。

这是一个相信的例子，显示了如何使用 Map ：

 枚举AnimalType {CAT，DOG} 
 interface Animal {} 
 class Cat implements Animal {} 
 class Dog implements Animal {} 
 
 public class AnimalFactory {
 
 private static final Map< AnimalType，Animal> enumMap 
 = new EnumMap< AnimalType，Animal>（AnimalType.class）; 
 //对
 private static final Map< String，Animal> stringMap 
 = new HashMap< String，Animal>（）; 
 
 static {
 enumMap.put（AnimalType.CAT，new Cat（））; 
 enumMap.put（AnimalType.DOG，new Dog（））; 
 stringMap.put（CAT，new Cat（））; 
 stringMap.put（DOG，new Dog（））; 
} 
 public static Animal（String type）{
 Animal result = enumMap.get（AnimalType.valueOf（type））; 
 Animal result2 = stringMap.get（type）; 
 return result; 
} 
} 
  

假设 AnimalType 枚举和映射只能由 AnimalFactory 使用来创建动物，而不在其他地方。

解决方案

如果所有有效的键都可以使用，那么 Map 枚举，我会使用它，因为它确保你总是使用一个有效的值。

它也可以避免混乱，因为String可以用于许多事情，很容易将Animal字符串转换为用于其他字符串的字符串。由于枚举类型通常不能与其他类型互换（除非使用通用接口），因此编码错误的可能性较小。

I'm trying to weigh the pros and cons of using an EnumMap over a HashMap. Since, I will always be looking up using a String, it seems that a HashMap with a String key would be the right choice. However, an EnumMap seems like better design because it conveys my intent to restrict keys to a specific enumeration. Thoughts?

Here is a make-believe example, showing how I will be using the Map:

enum AnimalType { CAT, DOG }
interface Animal {}
class Cat implements Animal {}
class Dog implements Animal {}

public class AnimalFactory {

    private static final Map<AnimalType, Animal> enumMap 
            = new EnumMap<AnimalType, Animal>(AnimalType.class);
    // versus
    private static final Map<String, Animal> stringMap 
            = new HashMap<String, Animal>();

    static {
        enumMap.put(AnimalType.CAT, new Cat());
        enumMap.put(AnimalType.DOG, new Dog());
        stringMap.put("CAT", new Cat());
        stringMap.put("DOG", new Dog());
    }
    public static Animal create(String type) {
        Animal result = enumMap.get(AnimalType.valueOf(type));
        Animal result2 = stringMap.get(type);
        return result;
    }
}

Assume that the AnimalType enum and map will ONLY be used by the AnimalFactory to create animals and nowhere else.

Which Map should I use?

解决方案

If all valid keys can be enumerated, I would use that as it ensures you are always working with a valid value.

It can also avoid confusion as String can be used for lots of things and is easy to turn an "Animal" string into a string used for something else. As enum types are not interchangable with other types in general (unless you use a common interface), there is less chance of error in coding.

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