Define constant "Value" for enum string values

Question

For the enum defined as below

public enum Cars {

    SWIFT("Maruti"),
    DZIRE("Maruti"), 
    CIAZ("Maruti"), 
    I10("Hyundai"), 
    CRETA("Hyundai");

    String company;
    Cars(String company){
        this.company = company;
    }   
}

There is Sonar error

Define a constant instead of duplicating this literal "Maruti" 3 times.

If we define static string, it fails to compile

Cannot reference a field before it is defined

Solution 1:

public enum Cars {

    SWIFT(CarsString.MARUTI.companyName),DZIRE("Maruti"), I10("Hyundai"), CRETA("Hyundai");

    static String MARUTI = "Maruti";
    String company;
    Cars(String company){
        this.company = company;
    }

    enum CarsString {
        MARUTI("maruti"),
        HYUNDAI("Hyundai");
        String companyName;
        CarsString(String companyName){
            this.companyName = companyName;
        }
    }
}

Solution 2:

Not sure if this is the way we do it. When it is not referenced by Cars.MARUTI, it errors out Cannot reference a field before it is defined.

public enum Cars {

    SWIFT(Cars.MARUTI),DZIRE(Cars.MARUTI), I10("Hyundai"), CRETA("Hyundai");

    public static final String MARUTI = "Maruti";
    String company;
    Cars(String company){
        this.company = company;
    }
 }

I have 10 enums in similar state and the above solution 1 didn't much encourage me. Solution 2 solves the purpose,

but why should we refer by Cars.MARUTI and not MARUTI directly? is that a limitation ?

How could we refer a constant value in enum ?

Answer 1

What about defining the company in its own Enum? For example:

public enum Car {
    SWIFT(Company.MARUTI),
    DZIRE(Company.MARUTI),
    CIAZ(Company.MARUTI),
    I10(Company.HYUNDAI),
    CRETA(Company.HYUNDAI);

    Company company;

    Cars(Company company) {
        this.company = company;
    }
}

public enum Company {
    HYUNDAI("Hyundai"),
    MARUTI("Maruti");

    String name;

    Company(String name) {
        this.name = name;
    }
}

Update: improved naming conventions according to comment of @Basil Bourque, thx!

Answer 2

You need to know how enum works internally. If you look at the byte code of your enum you will have the answer.

 6: iconst_0
   7: ldc           #19                 // String Maruti
   9: invokespecial #21                 // Method "<init>":(Ljava/lang/String;ILjava/lang/String;)V
  12: putstatic     #25                 // Field SWIFT:Labc/Cars;
  15: new           #1                  // class abc/Cars
  18: dup
  19: ldc           #27                 // String DZIRE
  21: iconst_1
  22: ldc           #19                 // String Maruti
  24: invokespecial #21                 // Method "<init>":(Ljava/lang/String;ILjava/lang/String;)V
  27: putstatic     #28                 // Field DZIRE:Labc/Cars;
  30: new           #1                  // class abc/Cars
  33: dup
  34: ldc           #30                 // String CIAZ
  36: iconst_2:

From the above byte code (which was generated from Cars enum), we can have a class which will be similar to the Cars enum

class Foo {
    public static Cars SWIFT = new Cars("Maruti");
    public static Cars DZIRE = new Cars("Maruti");
    public static Cars CIAZ = new Cars("Maruti");
}

Now if you change the code to :

class Cars {

    public static Cars SWIFT = new Cars(MARUTI); //statement-1
    public static Cars DZIRE = new Cars(MARUTI); //statement-2
    public static Cars CIAZ = new Cars(MARUTI); //statement-3

    public static String MARUTI = "Maruti"; // statement-4


    private String name;

    public Cars(String name) {
        this.name = name;
    }
}

It will give you the same error message because you are using the variable before it is defined. If we move up the statement-4 before statement-1 it will work. But it is only possible in class but enum does not allow you as the first statement.So in your case you can solve like :

enum Cars {

    SWIFT(Constants.MARUTI), DZIRE(Constants.MARUTI), I10("Hyundai"), CRETA("Hyundai");

    String company;

    Cars(String company) {
        this.company = company;
    }

    private static class Constants {

        public static String MARUTI = "Maruti";
    }
}