I have a couple of questions about abstract with default implementation

[Robert Field]

On 12/16/11 9:14 PM, bitter_fox wrote:
> I have a couple of questions about abstract with default implementation
>
> *Revision of javac is 1245.
>
> 1.Does "default implementation" work in extending abstract class?
> interface A
> {
>      void a() default {}
> }
> interface B
> {
>      void a(); // B#a is an abstract method same as C#a
> }
> abstract class C
> {
>      public abstract void a();
> }
>
> class D implements A, B // OK
> {}
> class E extends C implements A // Compile error
> {}
>
> Is it correct that E makes the compile error:
> Main.java:16: error: E is not abstract and does not override abstract
> method a() in C
> class E extends C implements A // Compile error

Yes, the rule is "class always wins", that includes abstract class methods.

>
> 2.Can I use default implementation for "abstract method" in interface?
> The methods are abstract in interface, whether there is "abstract" or not.
> (I know that using "abstract" in interface is not recommended.)
> So, these will be same:
> interface A
> {
>      void a() default {}
> }
> interface B
> {
>      abstract void a() default {} // (1)
> }
> However, (1) makes the compile error:
> Main.java:25: error: abstract methods cannot have a body
>          abstract void a() default {} // (1)

I don't believe the abstractness of default methods is completely nailed 
down.  But our model of it for the current implementation is that 
default methods are not abstract (even though they are in an 
interface).  Two possible models: (1) now three options: 
abstract/concrete/default; or (2) default methods are concrete.

-Robert

>
> Thanks,
> bitter_fox
>