问题

I have multiple enum classes . For example

public class enum Animal {
DOG,
LION;
}
public class enum Bird {

OSTRICH,
CROW };
}
I want to have a Map<String, Enums > where i can store these enum classes as values and then fetch them based on keys . For example
Map<String, Enumclass> such that it gives me the Enum when i pass the key to the Map. For example map.get("Animal") should return me the enum Animal and then i can do operations like Animals.valueOf();

I was able to store the enums in a private Map<String, Class<? extends Enum>> Map; but not able to retreive and cast it back to the proper enum classes. Is it possible to do this

   public class enum Animal { 
        DOG,
        LION;
} 
    public class enum Bird { 

     OSTRICH,
     CROW };
}

答案1

得分: 3

You will need to have your enums implement a common interface like so:

import java.util.*;

public class Zoo {
    private static final Map<String, ZooAnimal> animals;

    static {
        Map<String, ZooAnimal> tmp = new HashMap<>();
        tmp.put("CHEETAH", Cat.CHEETAH);
        tmp.put("LION", Cat.LION);
        tmp.put("PANTHER", Cat.PANTHER);
        tmp.put("TIGER", Cat.TIGER);
        tmp.put("HAWK", Bird.HAWK);
        tmp.put("OSTRICH", Bird.OSTRICH);
        tmp.put("OWL", Bird.OWL);
        animals = Collections.unmodifiableMap(tmp);
    }

    public static void main(String[] args) {
        ZooAnimal animal = animals.get("PANTHER");
        if (animal != null && animal instanceof Cat) {
            // A panther is a cat
            System.out.printf("A %s is a cat%n", animal.getName().toLowerCase());
        }
    }

    private interface ZooAnimal {
        String getName();
    }

    public enum Cat implements ZooAnimal {
        CHEETAH, LION, PANTHER, TIGER;

        @Override
        public String getName() {
            return this.name();
        }
    };

    public enum Bird implements ZooAnimal {
        HAWK, OSTRICH, OWL;

        @Override
        public String getName() {
            return this.name();
        }
    };
}

If you want the values, you can use the generic Enum class:

import java.util.*;

public class Zoo {
    private static final Map<String, Class<? extends Enum<?>>> animals;

    static {
        Map<String, Class<? extends Enum<?>>> tmp = new HashMap<>();
        tmp.put("BIRD", Bird.class);
        tmp.put("CAT", Cat.class);
        animals = Collections.unmodifiableMap(tmp);
    }

    public static void main(String[] args) {
        Class<? extends Enum<?>> animal = animals.get("CAT");
        // Print the values
        for (Enum<?> c : animal.getEnumConstants()) {
            System.out.println(c.name()); // CHEETAH, LION, PANTHER, TIGER
        }
    }

    public enum Cat {
        CHEETAH, LION, PANTHER, TIGER;
    };

    public enum Bird {
        HAWK, OSTRICH, OWL;
    };
}

import java.util.*;

public class Zoo {
    private static final Map<String, ZooAnimal> animals;

    static {
        Map<String, ZooAnimal> tmp = new HashMap<>();
        tmp.put("CHEETAH", Cat.CHEETAH);
        tmp.put("LION", Cat.LION);
        tmp.put("PANTHER", Cat.PANTHER);
        tmp.put("TIGER", Cat.TIGER);
        tmp.put("HAWK", Bird.HAWK);
        tmp.put("OSTRICH", Bird.OSTRICH);
        tmp.put("OWL", Bird.OWL);
        animals = Collections.unmodifiableMap(tmp);
    }

    public static void main(String[] args) {
        ZooAnimal animal = animals.get("PANTHER");
        if (animal != null && animal instanceof Cat) {
            // A panther is a cat
            System.out.printf("A %s is a cat%n", animal.getName().toLowerCase());
        }
    }

    private interface ZooAnimal {
        String getName();
    }

    public enum Cat implements ZooAnimal {
        CHEETAH, LION, PANTHER, TIGER;

        @Override
        public String getName() {
            return this.name();
        }
    };

    public enum Bird implements ZooAnimal {
        HAWK, OSTRICH, OWL;

        @Override
        public String getName() {
            return this.name();
        }
    };
}

import java.util.*;

public class Zoo {
    private static final Map<String, Class<? extends Enum<?>>> animals;

    static {
        Map<String, Class<? extends Enum<?>>> tmp = new HashMap<>();
        tmp.put("BIRD", Bird.class);
        tmp.put("CAT", Cat.class);
        animals = Collections.unmodifiableMap(tmp);
    }

    public static void main(String[] args) {
        Class<? extends Enum<?>> animal = animals.get("CAT");
        // Print the values
        for (Enum<?> c : animal.getEnumConstants()) {
            System.out.println(c.name()); // CHEETAH, LION, PANTHER, TIGER
        }
    }

    public enum Cat {
        CHEETAH, LION, PANTHER, TIGER;
    };

    public enum Bird {
        HAWK, OSTRICH, OWL;
    };
}

答案2

得分: 0

* 更新我的答案，因为问题附带了更多解释。

我将提供另一种方法，即向枚举添加另一个维度以指示动物类型，在这种情况下，您无需转换为多个枚举：

public enum AnimalType
{
    BIRD, CAT;
}
public enum Animal
{
    CHEETAH(AnimalType.CAT, "猎豹"),
    LION(AnimalType.CAT, "狮子"),
    HAWK(AnimalType.BIRD, "鹰"),
    OWL(AnimalType.BIRD, "猫头鹰");

    private AnimalType type;
    private String name;

    Animal(AnimalType type, String name) {
        this.type = type;
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public AnimalType getType() {
        return type;
    }

    public static Optional<Animal> fromName(String name) {
        return Arrays.stream(Animal.values())
            .filter(a -> a.name.equals(name))
            .findFirst();
    }

    public static List<Animal> fromType(AnimalType type) {
        return Arrays.stream(Animal.values())
            .filter(a -> a.type == type))
            .collect(Collectors.toList());
    }
}

public enum AnimalType 
{
    BIRD, CAT;
}
public enum Animal 
{
    CHEETAH(AnimalType.CAT, "Cheetah"),
    LION(AnimalType.CAT, "Lion"),
    HAWK(AnimalType.BIRD, "Hawk"),
    OWL(AnimalType.BIRD, "Owl");
 
    private AnimalType type;
    private String name;
 
    Animal(AnimalType type, String name) {
        this.type = type;
        this.name = name;
    }
 
    public String getName() {
        return name;
    }

    public AnimalType getType() {
        return type;
    }

    public static Optional<Animal> fromName(String name) {
        return Arrays.stream(Animal.values())
            .filter(a -> a.name.equals(name))
            .findFirst();
    }

    public static List<Animal> fromType(AnimalType type) {
        return Arrays.stream(Animal.values())
            .filter(a -> a.type == type))
            .collect(Collectors.toList());
    }
}

答案3

得分: 0

以下是翻译好的部分：

• "There doesn't appear to be an exact solution to what you're looking to achieve." -> "似乎没有确切的解决方案来实现你所希望的。"
• "Essentially, I believe that since an enum is considered a static object, you cannot cast the static reference into a new object." -> "基本上，我认为由于 enum 被视为 static 对象，你无法将静态引用转换为新对象。"
• "You would have to use a Class<Animal> type." -> "你需要使用 Class<Animal> 类型。"
• "And, at that rate, you're better off just utilizing the Enum class." -> "而且，在这种情况下，最好直接使用 Enum 类。"
• "Here is a tutorial on Java reflection with enums, for this specific requirement." -> "这里有一个关于在特定需求下使用 enums 的Java反射教程。"
• "Examining Enums (The Java&trade; Tutorials &gt; The Reflection API &gt; Arrays and Enumerated Types)" -> "查看Enums (Java&trade;教程 &gt; 反射API &gt; 数组和枚举类型)"
• "Since you know that your map values are going to be enum objects, you can utilize the Enum#valueOf method, to obtain a single value." -> "由于你知道你的映射值将是 enum 对象，你可以利用 Enum#valueOf 方法来获取单个值。"
• "If you want a list of values, similar to the values method, you can use an array of Enum and utilize the Class#getEnumConstants." -> "如果你想要一个类似于 values 方法的值列表，你可以使用 Enum 数组并利用 Class#getEnumConstants。"
• "java\nMap<String, Class<? extends Enum>> map = new HashMap<>();\nmap.put("Animal", Animal.class);\nmap.put("Bird", Bird.class);\nfor (Enum value : map.get("Animal").getEnumConstants()) \n System.out.println(value.name());\n" -> "java\nMap<String, Class<? extends Enum>> map = new HashMap<>();\nmap.put("Animal", Animal.class);\nmap.put("Bird", Bird.class);\nfor (Enum value : map.get("Animal").getEnumConstants()) \n System.out.println(value.name());\n"

Map<String, Class<? extends Enum>> map = new HashMap<>();
map.put("Animal", Animal.class);
map.put("Bird", Bird.class);
for (Enum value : map.get("Animal").getEnumConstants()) 
    System.out.println(value.name());

答案4

得分: -1

我通过Reflections找到了一个解决方案。可以这样做：

Map<String, Class<? extends Enum<?>>> errorCodes = errorCodeMap.getErrorCodeMap();
Class<? extends Enum<?>> enumClass = errorCodes.get(code.substring(0, 1));
Enum<?>[] enumConstants = enumClass.getEnumConstants();
Class<?> actualEnumClass = enumConstants[0].getDeclaringClass();
StringBuilder errorCode = new StringBuilder().append(prefix).append(code);
Enum<?> errorEnum = Enum.valueOf(actualEnumClass.asSubclass(Enum.class), errorCode.toString());

Map<String, Class<? extends Enum<?>>> errorCodes = errorCodeMap.getErrorCodeMap();
Class<? extends Enum<?>> enumClass = errorCodes.get(code.substring(0, 1));
Enum<?>[] enumConstants = enumClass.getEnumConstants();
Class<?> actualEnumClass = enumConstants[0].getDeclaringClass();
StringBuilder errorCode = new StringBuilder().append(prefix).append(code);
Enum<?> errorEnum = Enum.valueOf(actualEnumClass.asSubclass(Enum.class), errorCode.toString());