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javaenums
Babak
Babak

Reputation: 487

Assign Enum Values in Java

If I have two enums, say:

public enum E1 {
    A, B
}

public enum E2 {
    A, B
}

Is there any way I can assign a value of the enum type E2 to the value of type E1, like this:

E2 var = E1.B;

(Assuming that I know in advance that B exists in both enums)

Edit:

I understand that Java doesn't allow this. Maybe I should explain this as well then. I have a variable (x) of type enum E1 (it can be A or B). For the task that I'm trying to achieve, I need to have another variable of type enum E2 with the same value. The way that I'm handling this right now is basically:

if (x == E1.A) {
    E2 var = E2.A;
} else {
    E2 var = E2.B;
}

So I guess what I'm asking this is that is there any nicer way to do this?

Upvotes: 1

Views: 3477

Answers (6)

Jarvis Cochrane
Jarvis Cochrane

Reputation: 101

Since you can define enums as 'lightweight classes' conforming to interfaces with their own properties and methods, you can write up your combining rules something like this:

Upholstery.java

import java.util.List;

public interface Upholstery {

    public List<Material> combinesWith();

}

Material.java

import java.util.List;

public interface Material {

    public List<Upholstery> combinesWith();
}

Upholsteries.java

import java.util.Arrays;
import java.util.List;

public enum Upholsteries implements Upholstery {
    SATIN {
        @Override
        public List<Material> combinesWith() {
            return Arrays.asList(Materials.PLASTIC);
        }
    },
    LEATHER {
        @Override
        public List<Material> combinesWith() {
            return Arrays.asList(Materials.MAHOGANY);
        }
    }
}

Materials.java

import java.util.Arrays;
import java.util.List;

public enum Materials implements Material {
    MAHOGANY {
        @Override
        public List<Upholstery> combinesWith() {
            return Arrays.asList(Upholsteries.SATIN,
                                 Upholsteries.LEATHER);
        }
    },
    PLASTIC {
        @Override
        public List<Upholstery> combinesWith() {
             return Arrays.asList(Upholsteries.SATIN);
        }
    }
}

Obviously, you could add additional methods to the interfaces, or modify the signature of combinesWith() to implement more complex logic - e.g. combinesWith(FurnitureType f, double budget).

Upvotes: 0

ΦXocę 웃 Пepe&#250;pa ツ
ΦXocę 웃 Пepe&#250;pa ツ

Reputation: 48258

The short answer is NO, java is not allowing that

I need more info about what exactly you need to do, but you can achieve something similar doing something like this

public static void main(String[] args) {

    E2 myE2 = E2.valueOf(E1.A.name());
    System.out.println(myE2);
    }

    enum E1 {
    A, B
    }

    enum E2 {
    A, B
    }

and note that will work ONLY because the field A is defined in both enums, otherwise is not going to work failing with an java.lang.IllegalArgumentException: No enum constant ...

but this workaround is exactly what you post when you say

(Assuming that I know in advance that B exists in both enums)

Upvotes: 0

Timothy Truckle
Timothy Truckle

Reputation: 15622

You can do this indirectly if you let both enum implement the same interface:

interface CommonEnumInterface{}

public enum E1 implements  CommonEnumInterface{
A, B
} 

public enum E2 implements  CommonEnumInterface{
C, D
}

CommonEnumInterface myE  = E1.A;
myE  = E2.D;

Upvotes: 2

Michael Lihs
Michael Lihs

Reputation: 8220

Well - looking at your second snippet, what you could do is to define E2 as

enum E2 {
    A, B
}

and E1as

enum E1 {

    A(E2.A), B(E2.B);

    private E2 e2;

    E1(E2 e2) {
        this.e2 = e2;
    }

    public E2 getE2() {
        return e2;
    }

}

like this you can simply write your if statement as

E2 var = x.getE2();

The idea behind this solution is, that enums like any other class in Java can have properties (private E2 e2), constructors (E1(E2 es) {...}) and methods (public E2 getE2()). Like that you can "add" any other values to your enum instances and use a getter to query them later on.

Upvotes: 0

nasukkin
nasukkin

Reputation: 2540

No.

E1 and E2 are two different enum types. Imagine you were developing a card game application and you had an enum for Suite and an enum for Rank. What you are asking is equivalent to trying to say that a card can have a Suite of Rank.TEN or a Rank of Suite.HEARTS. It just doesn't make sense, and isn't how enums work.

Upvotes: 3

M. Rizzo
M. Rizzo

Reputation: 2251

Yeah the answer as commented above, is you can't do it.

Enums in Java are type-safe and have their own namespace. It means your enum will have a type for example "Currency" and you can not assign any value other than specified in Enum Constants. E1 is E1 and E2 is E2 namespace.

Upvotes: 0

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