CODEWITHSUNDEEP
javaenumsinterface
LeO
LeO

Reputation: 5248

Java generic Types for method signature on enums implementing

I basically want to have an enum with specific methods, e.g.

public interface PropertyTypeMethods {
    public int getTypeId();

    public void setTypeId(Integer typeId);
}

and something like

public enum BasePropertyTypes implements PropertyTypeMethods {

ONE, TWO;

private int typeId;

@Override
public int getTypeId() {
    return typeId;
}

@Override
public void setTypeId(Integer typeId) {
    this.typeId = typeId;
}

}

as well as an extended version of this enum, e.g.

public enum ExtendedPropertyTypes implements PropertyTypeMethods {
HUNDRED, THOUSEND; 
// same as above
}

which would result in ONE.setTypeId(1) ==> ONE.getTypeId()==1 //true. That is the basic concept. But now I want to call a generic method like e.g.

private <E extends Enum<E> & PropertyTypeMethods> void initEnum(Enum<E> curType) {
   // the below approach does not work :-/
   curType.setTypeId(1); // or any other reasonable value....

But somehow I cannot figure out what the correct method signature would be. Following this question I figured at least some part of the puzzle - but still don't get it for the method signature. Still it remains unclear how to specify curType properly in the signature to execute an appropriate call.

Upvotes: 1

Views: 917

Answers (2)

ttzn
ttzn

Reputation: 2613

This will work :

private <E extends Enum<E> & PropertyTypeMethods> void initEnum(E curType) {
  curType.setTypeId(1);
}

However, I don't think it's a good idea to make mutable Enums (they're meant to be labels over constant values, not state-carrying singletons). Furthermore, you shouldn' write methods that require an Enum parameter when all they should care about is its interface : 

// This will be easier to work with down the road
private void initEnum(PropertyTypeMethods curType) {
  curType.setTypeId(1);
}

Upvotes: 2

M.F
M.F

Reputation: 443

The correct signature would simply be

private void initEnum(PropertyTypeMethods onject) {
    object.setTypeId(1);
}

But as Andy Turner mentioned, enums are expected to be immutable, i.e. only final immutable field. Therefore, enums also have a constructor Enum Types.

If you have more complex enums, it is a common way to implement them as follows

public enum BasePropertyTypes implements PropertyTypeMethods {
   ONE (new PropertyTypeMethods() {
          @Override
          public int getTypeId() {
              return 1;
          }
     });

    private final PropertyTypeMethods m;

    BasePropertyTypes(PropertyTypeMethods m) {
       this.m = m;
    }

   @Override
   public int getTypeId()
   {
      return this.m.getTypeId();
   }
}

But from your example, I would suggest to review your actual issue. Propably enums are not the proper way at all.

Upvotes: 1

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