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jilt3d
jilt3d

Reputation: 4034

General method for creating enum instances from String

Let say I have two enum classes which implement a Foo interface

public enum Enum1 implements Foo {
  ENUM1_CONST1,
  ENUM1_CONST2;
}

public enum Enum2 implements Foo {
  ENUM2_CONST1,
  ENUM2_CONST2;
}

How can I create a type-safe implementation of a method that takes a string as a parameter which string matches any of the enum constant's name and returns a Foo instance which could be any of the constants from both enum definitions.

In other words: Foo foo1 = holyGrailMethod("ENUM1_CONST1"); Foo foo2 = holyGrailMethod("ENUM1_CONST2"); Foo foo3 = holyGrailMethod("ENUM2_CONST1"); Foo foo4 = holyGrailMethod("ENUM2_CONST2");

Upvotes: 0

Views: 587

Answers (1)

Pshemo
Pshemo

Reputation: 124215

Just iterate over all your enum types (you can place them in some collection) and invoke 

Enum.valueOf(EnumType, nameOfConstant)

But be careful because this method will throw java.lang.IllegalArgumentException if checked enum type will not have described field.

Other way would be just iterating over collection of your enum types, getting its values (you can use Class.getEnumConstants here) and checking if name of enum constant is same as name passed by user. 

public static Enum<?> getEnumFromMany(Collection<Class<?>> enums, String value) {
    for (Class<?> enumType : (Collection<Class<?>>) enums)
        if (enumType.isEnum()) {
            @SuppressWarnings("unchecked")
            Class<Enum<?>> clazz = (Class<Enum<?>>) enumType;
            for (Enum<?> en : clazz.getEnumConstants()) {
                if (en.name().equals(value))
                    return en;
            }
        }
    return null;
}

I used Collection> instead of Collection<Class<Enum<?>>> because generics are not covariant so Collection<Class<Enum<?>>> would not let you add Class<YourEnum>> to itself.

Usage example 

public enum DaysILike {
    FRIDAY, SATURDAY, SUNDAY
}

public enum DaysIDontLike {
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY
}

public static void main(String[] args) {
    List<Class<?>> enums = new ArrayList<>();
    enums.add(DaysIDontLike.class);
    enums.add(DaysILike.class);
    String yourString = "THURSDAY";
    Enum<?> en = getEnumFromMany(enums, yourString);
    System.out.println(en + " from " + en.getClass());
}

Output: THURSDAY from class SO22436944$DaysIDontLike

Upvotes: 3

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