Unique enum member values

Question

My problem: I want to specify a 1 to 1 connection between two enums. basically:

enum MyEnum{

    ENUM_VALUE_1,
    ENUM_VALUE_2,
    ENUM_VALUE_3,

}

enum          


        

Answer 1

How about this:

public enum MyEnum {

    ENUM_VALUE_1,
    ENUM_VALUE_2,
    ENUM_VALUE_3,

}

// All enums taken.
private static final Set taken = EnumSet.noneOf(MyEnum.class);

enum MyOtherEnum {

    OTHER_ENUM_VALUE_1(MyEnum.ENUM_VALUE_3),
    OTHER_ENUM_VALUE_2(MyEnum.ENUM_VALUE_1),
    OTHER_ENUM_VALUE_3(MyEnum.ENUM_VALUE_2),
    OTHER_ENUM_VALUE_4(MyEnum.ENUM_VALUE_2);

    private MyEnum pair;

    MyOtherEnum(MyEnum pair) {
        if (taken.contains(pair)) {
            throw new IllegalArgumentException("Cannot pair the same MyEnum with two other enums! " + this);
        }
        taken.add(pair);
        this.pair = pair;
    }

}

public void test() {
    System.out.println("Hello: " + MyOtherEnum.OTHER_ENUM_VALUE_4);
}