enums & abstract modifier

[Marco Persi]

Hi guys,

probably one of you may answer me a question.
I'm reading: http://jcp.org/aboutJava/communityprocess/jsr/tiger/enum.html

There you may read, that enum declarations may NOT use the class modifier abstract, unless they contain constant specific class bodies for every enum constant......

In my opinion I have implemented exactly that:

package ch.persi.java.tiger.enumeratedTypes;
 
public enum Place {
    ROTKREUZ("6343")
    {
        public void doSomething()
        {System.out.println("...doing something..");}
    },     
    ALTDORF("6460")
    {
        public void doSomething()
        {System.out.println("...doing something..");}
        
    },  // another, yep you see..it works
    LUZERN("6300")
    {
        public void doSomething()
        {System.out.println("...doing something..");}
    };
    
    
    Place(String id)
    {
        System.out.println(id);
    }
    
   public abstract void doSomething();   
}

===> Well, if you try to compile this enum, it works. No problem at all.
BUT: try to declare the enum Place as abstract (since it contains an abstract method) and you'll get a compiler error (...at least within my Netbeans 4.0).

I'm still wondering...; well, let's try the plain javac .....we will see

regards
marco
[ February 05, 2005: Message edited by: Jim Yingst ]

[Bilal Al-Sallakh]

Tiger doesn't support enums hierarchy --> an enum is effectively final. But since value-specific methods through anonymous inner classes will be bowerfull, it allows this special type of subclassing --> it allows abstract methods, yet the enum itself still final (can't be subclassed) --> can't be declared abstract (nor final!).

[Jim Yingst]

Marco, I edited your post above to include [code] tags - this preserves the indentation in your code, making it more readable.

Note that the page at jcp.org is part of the earlier documentation for what was, at the time, a proposed new language feature. Now, enums are an actual existing language feature - but the way they work has been modified a bit since the initial proposal. You're looking at old documentation. A better reference now is at

http://java.sun.com/j2se/1.5.0/docs/guide/language/enums.html

Basically, Sun decided (correctly, I think) tht it didn't make any sense for the enum itself to be declared abstract, since it's impossible for any code outside the enum to extend it. Only the method is abstract, and only code within the enum declaration is capable of overriding it.