While implementing an interface in an enum, why eclipse automatically puts a semicolon before the interface method being overridden?

Question

I have an interface and an enum

I am implementing the interface in the enum

I am using eclipse as my IDE

Following is my interface file -

ITrafficSignal.java -->

public interface ITrafficSignal {
    public void showAction();
}

Following is my enum file -

ETrafficSignal.java -->

public enum ETrafficSignal implements ITrafficSignal {
    ;

    @Override
    public void showAction() {

    }
}

here the ; in line 2 is being automatically being put by eclipse

If I remove ;, then in the method being implemented -

public void showAction()

is having a red line below the keyword void and the error says -

Multiple markers at this line 
- implements ITrafficSignal.showAction
- Syntax error on token "void", volatile expected

I am unable to understand this.

Slaw · Accepted Answer · 2020-03-18T15:28:51.107

That's simply the syntax of enum types. From §8.9 Enum Types of the Java Language Specification:

EnumDeclaration:
  {ClassModifier} enum TypeIdentifier [Superinterfaces] EnumBody

And the syntax of EnumBody is:

EnumBody:
  { [EnumConstantList] [,] [EnumBodyDeclarations] }

EnumConstantList:
  EnumConstant {, EnumConstant}

EnumConstant:
  {EnumConstantModifier} Identifier [( [ArgumentList] )] [ClassBody]

EnumConstantModifier:
  Annotation

And finally the syntax of EnumBodyDeclarations is:

EnumBodyDeclarations:
  ; {ClassBodyDeclaration}

As you can see, the above shows that the enum body declarations must be preceded by a semicolon (;) separating it from the enum constants. Unlike the EnumConstantList the semicolon is not optional¹. This means the semicolon must be present if there's enum body declarations regardless of there being any enum constants declared, though I personally don't see the point in having an enum type without constants.

^{1. The entire EnumBodyDeclarations is optional, however, meaning if there's no body declarations then the semicolon can be omitted.}

Good answer, somehow I knew that it was needed, but never cared to look at the spec. Also to the statement: *though I personally don't see the point in having an enum type without constants.*, [`enum`s can (sadly) be used like static classes for holding utility methods](https://stackoverflow.com/questions/4992893/using-enums-to-implement-utility-classes-and-singletons) — Lino, Mar 18 '20 at 15:27

While implementing an interface in an enum, why eclipse automatically puts a semicolon before the interface method being overridden?

1 Answers1