How to add common methods for a few Java enums? (abstract class ancestor?)

Question

I have a few Java enums as such

public enum Aggregation
{
    MORTGAGE( \"Mortgage\" ),
    POOLS( \"Pools\" ),
    PORTFOLIO( \"Portfolio\" );

    private         


        

Answer 1

You can achieve this with Java 8 default interface methods:

public class test
{
    public static void main (String[] arguments) throws Exception
    {
        X.A.foo ();
        Y.B.foo ();
    }
}

interface MyEnumInterface
{
    String getCommonMessage ();
    String name ();

    default void foo ()
    {
        System.out.println (getCommonMessage () + ", named " + name ());
    }
}

enum X implements MyEnumInterface
{
    A, B;

    @Override
    public String getCommonMessage ()
    {
        return "I'm an X";
    }
}

enum Y implements MyEnumInterface
{
    A, B;

    @Override
    public String getCommonMessage ()
    {
        return "I'm an Y";
    }
}

Note that the interface doesn't know it will be implemented by enums, so it cannot use Enum methods on this in the default methods. However, you may include those methods in the interface itself (like I did with name()) and then use them normally. They will be "implemented" for you by Enum when you declare an enumeration.