How can I override toString() Method for all enum classes?

Question

Is it possible to override the method toString for all Enum classes, rather than overriding it only in the enum class. Example:

Coins.java:

enum Coins { PENNY(1), POUND(100), NOTE(500); 

    private int value;

    Coins(int coinValue) {
         value = coinValue;
    }
     [...] // Other code

    public String toString() {
         return name().charAt(0) + name().substring(1).toLowerCase();
    }
}

DaysOfWeek.java:

enum DaysOfWeek { MONDAY(1), TUESDAY(2), WEDNESDAY(3);
   
     private int dayID;

     DaysOfWeek(int ID) {
        dayID = ID;
     }
       [...] // Other code

     public String toString() {
         return name().charAt(0) + name().substring(1).toLowerCase();
     }
 }

Currently, I have to override toString() in each enum class. Can I create a generic toString method that will override all classes that are of enum type without actually writing toString in every enum type class?

Answer 1

No. You can't override the system's Enum class, and you cannot make a subclass from which all of your Enums inherit from as it is a language feature with a lot of special rules. However, you can make a static helper method:

public class Utils {
  public static String toEnumString(Enum<?> inputEnum) {
    return inputEnum.name().charAt(0) + inputEnum.name().substring(1).toLowerCase();
  }
}

This can be used in two different ways:

1. You can still override toString() in your enums, but with a lot less chance for copy paste error, and the ability to change it everyone with one code change. e.g.

   enum Coins { PENNY(1), POUND(100), NOTE(500); 
   
     // snip 
     public String toString() {
       return Utils.toEnumString(this);
     }
   }
   

2. You can use it in other methods, for example:

   System.out.println(Utils.toEnumString(Coins.PENNY));
   preparedStatement.setString(1, Utils.toEnumString(Coins.POUND));
   

---

You can also use Apache Commons or Google Guava to do the same thing, if you want to add another library to your project:

• Apache Commons: WordUtils.capitalizeFully
• Guava: CaseFormat.UpperCamel

Answer 2

I'd make a delegate/utlity/helper that all the enum toString() methods call. This avoids having to call a utility class whenever you wish to convert to a String.

private static class CommonEnumToString {
    static String toString(Enum<?> e) {
        return e.name().charAt(0) + e.name().substring(1).toLowerCase();
    }
}

Update the toString() to call the helper

enum Coins {
    PENNY(1), POUND(100), NOTE(500);
    private int value;
    Coins(int coinValue) {
        value = coinValue;
    }
    public String toString() {
        return CommonEnumToString.toString(this);
    }
}

enum DaysOfWeek {
    MONDAY(1), TUESDAY(2), WEDNESDAY(3);
    private int dayID;
    DaysOfWeek(int ID) {
        dayID = ID;
    }
    public String toString() {
        return CommonEnumToString.toString(this);
    }
}

Test

public static void main(String[] args) {
    System.out.println(DaysOfWeek.WEDNESDAY); // ==> Wednesday
    System.out.println(Coins.PENNY);          // ==> Penny
}