Enum with array/list values

enums, java

Solution

Enums can have data and behaviour much like classes. Something like this should work...

public enum RequiredFields {
    REQUIRED_FIELDS_FOR_DELIVERABLE_PRODUCTS( Fields.NAME, Fields.EMAIL, Fields.ADDRESS ),
    REQUIRED_FIELDS_FOR_DOWNLOADABLE_PRODUCTS( Fields.NAME, Fields.EMAIL );

    private List<String> fields;
    private RequiredFields(String... fields){
        this.fields = Arrays.asList(fields);
    }
    public List<String> getFields(){
        return fields;
    }
}

Further improvement:

In above code, the `fields` property is still mutable. Someone could do `REQUIRED_FIELDS_FOR_DELIVERABLE_PRODUCTS.getFields().add(..)` which would beat the whole purpose of having the `enum` in the first place.

Better implementation for the constructor would be:

private RequiredFields(String... fields){
    this.fields = ImmutableList.copyOf(fields); //com.google.common.collect.ImmutableList
}

Problem

``` if (isProductDeliverable) { REQUIRED_FIELDS = Arrays.asList(new String[] { Fields.NAME, Fields.EMAIL, Fields.ADDRESS }); } else { REQUIRED_FIELDS = Arrays.asList(new String[] { Fields.NAME, Fields.EMAIL }); } ``` Instead of this, I want to have a predefined enum with two fields - `REQUIRED_FIELDS_FOR_DELIVERABLE_PRODUCTS` and `REQUIRED_FIELDS_FOR_DOWNLOADABLE_PRODUCTS` I know the theory of enums but I've never used them so I cant figure out a way how to do this. Or maybe a way to ask for the required fields by passing this "isProductDeliverable" boolean and get the correct array of fields?

Original source