K&B Pg 666 Answer to Question #3

[Deepak Jain]

Hi,
K&B Pg 666 {Inner classes quiz} question #3
Given,
public interface Runnable{ void run();}
Which construts a anonymous inner class instance{Choose all that apply}
A. Runnable run = new Runnable() {}; // Incorrect because the anonymouse inner class implementer of Runnable does not implement run().
B. Runnable run = new Runnable(public void run() // Incorrect syntax
C. Runnable run = new Runnable {public void run();} // Incorrect syntax

D. Runnable run = new Runnable() {public void run();} // IS CORRECT. K&B says its incoorect syntax. K&B Errata on this site does not talk anything about Pg 666.

E. System.out.println(new Runnable() {public void run();}); // Correct. K&B also says its correct.
F. System.out.println(new Runnable {public void run();}); //Incorrect syntax.
Hence the answer to this question should be D & E. But K&B says 'E'.
Correct me!
Thanks
Deepak

[prajal Mehta]

hi,
I guess you have done some typing mistake while reproducing the question and options from the book.
The book gives option D as follows.

D. Runnable r = new Runnable() {public void run{}};

check the pair of curly braces after 'run' -- it is wrong syntax for any method.

[Deepak Jain]

How could i miss it Your correct.
Thanks
Deepak
[ December 04, 2007: Message edited by: Deepak Jain ]

[Marc Peabody]

That would have not been correct the other way either. Since you are creating an anonymous class, you are required to IMPLEMENT any necessary methods.

Neither one of these does that:

  
Runnable r = new Runnable() {public void run()};
Runnable r = new Runnable() {public void run{}};

It would need to look like this:

Runnable r = new Runnable() { public void run(){} };

The paranths () are needed as part of the method signature and the curly braces {} are needed to hold the method implementation - though in my case it is empty, so it's legal but not very useful.

You need both () and {} to implement the run method.