Defaults for Objects' methods

[Dan Smith]

On Jul 19, 2012, at 3:20 AM, Deepak S Patwardhan wrote:

> Hi all,
> 
> This has been previously discussed in the thread "defender methods and
> method of Object",
> http://mail.openjdk.java.net/pipermail/lambda-dev/2012-March/004582.html .
> 
> Consider the following (which compiles with lambda build 45)
> 
> public interface PrettyPrintable {
> 
>    public String prettyString();
> 
>    public String toString() default {
>        return prettyString();
>    }
> }
> 
> Since the (current) method resolution algorithm will never result in the
> invocation of the default body of toString() from this interface, shouldn't
> the above give a compilation error with the reason being unreachable code ?
> Basically, should we disallow interfaces to provide defaults for Object's
> methods ?

Yes, an error is the specified behavior.  So the EDR 2 specification, Part G, 9.4.3:

http://jcp.org/aboutJava/communityprocess/edr/jsr335/index2.html

This was a fairly recent decision, so it appears the compiler may not have caught up with it yet.

The question of how to handle Object methods has been discussed quite a bit by the Expert Group and will be discussed more.  The alternative of subclasses inheriting PrettyPrintable.toString rather than Object.toString is on the radar.  It's not a no-brainer, because it involves a fairly significant shift in the classes vs. interfaces model, but we know some people would really like it to work that way.

—Dan