Question about K&B book

[Serena Zhou]

Hi, I have a question about K&B book:
page 499 the code right below the exam watch:

Runnable r = new Runnable();

Shouldn't this result in compilation error?
Thanks!

[Nathaniel Stoddard]

You're correct. The compiler will freak out. Runnable is an interface, and I don't think you can create "subinterfaces" anonymously like we can anonymous classes.
I don't have the book laying around anymore so I can't tell you what the authors meant in the context. But what they might have been going for is something closer to:

public class Testing {
    public static void main(String[] args) {
        Runnable r = new Runnable() {
            public void run() {
                
            }
        };
    }
}

[Serena Zhou]

Thanks. but if you have pay attention to that ";" after Runnable(), you will find out that it is not the case.
The author might mean something like
Runnable r = new MyRunnable();// MyRunnable is a class that implements Runnable.

[Nathaniel Stoddard]

True. If MyRunnable truly is a class that implements the Runnable interface the program would compile. Since we only instantiate classes, using "new" on an interface type will always result in a compilation error unless we are talking about an anonymous class.

[Bert Bates]

Oops!
Serena you're right! It's amazing that on the 6th printing of this book there's still a few errors
It should be something like: Runnable r = new MyRunnable();
Thanks!