Toggleable Enum in Java

I came across this below code in my code base where we just want to toggle the enum value. If it is DEBIT return CREDIT, if CREDIT return DEBIT like below.

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enum DebitCreditCode implements Toggleable<DebitCreditCode> {
   DEBIT,
   CREDIT
} 

public static DebitCreditCode getReverseOfPaymentDebitCreditCode(DebitCreditCode
                                                                     debitOrCreditFromSummary) {
   if (debitOrCreditFromSummary != null && debitOrCreditFromSummary
                                                 .equals(DebitCreditCode.CREDIT)) {
      return DebitCreditCode.DEBIT;
   } else if (debitOrCreditFromSummary != null && debitOrCreditFromSummary
                                                        .equals(DebitCreditCode.DEBIT)) {
      return DebitCreditCode.CREDIT;
   }
   return null;
}

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This method is excellent and works as expected.

 

But…
If we want such requirement for any other enum,

• we have to define similar utility method for each enum and it is a repetitive job
• we will be landed up with duplicate code

So, to get rid of this, I have designed the below solution through which we can achieve the same without writing new method every time.

Step – 1 : Define this below interface in your common module. This is a one time job.

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interface Toggleable<T extends Enum<T>> {
   default T toggle() {
      final T[] enumConstants = (T[]) this.getClass().getEnumConstants();
      if (enumConstants == null) {
         throw new UnsupportedOperationException("Only enum can support toggling");
      }
      if (enumConstants.length != 2) {
         throw new UnsupportedOperationException("Enum must have 2 objects to support toggling");
      }
      return enumConstants[0] == this ? enumConstants[1] : enumConstants[0];
   }
}

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Step – 2 : Just implement the above interface to your enum class where you want this 
toggle/reverse feature like below :

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enum DebitCreditCode implements Toggleable<DebitCreditCode> {
   DEBIT,
   CREDIT
}

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Step – 3 : Call method toggle() on the enum object like

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final DebitCreditCode toggled = DebitCreditCode.DEBIT.toggle();
Assert.assertEquals(DebitCreditCode.CREDIT, toggled);
final DebitCreditCode original = toggled.toggle();
Assert.assertEquals(DebitCreditCode.DEBIT, original);

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Find complete code here