Re: When interface name used as type name

From:

"Jeff Higgins" <oohiggins@yahoo.com>

Newsgroups:

comp.lang.java.help

Date:

Sun, 24 Jun 2007 16:19:22 -0400

Message-ID:

<ilAfi.28$%e3.12@newsfe05.lga>

eastside wrote:

I have a question about how one conceptualizes the use of an interface name
when used as a type name.

In a book I have there's an code example illustrating the use of threads:

class RunPingPong implements Runnable { //use the Runnable interface

...

   RunPingPong(String whatToSay, int delayTime) { //CTOR

...

}

... (run method is here)

   public static void main(String[], args) {

       Runnable ping = new RunPingPong("ping", 33); //instantiate
object

       Runnable pong = new RunPingPong("pong", 100);

       new Thread(ping).start(); //submit thread

       new Thread(pong).start();

}

Here "Runnable," an interface, is also used as a type name for ping and
pong in the main method.

This is confusing to me because "Runnable" isn't a class. I take it ping
and pong are both objects? But what kind?

public class TypeTest
{
  public static void main(String[] args)
  {
    Runnable ping = new Ping();
    Runnable pong = new Pong();
    ping.run();
    pong.run();
  }

  static class Ping implements Runnable
  {
    int duration = 33;

    public void run()
    {
      System.out.println(duration);
    }
  }

  static class Pong implements Runnable
  {
    String utterance = "Pong";

    public void run()
    {
      System.out.println(utterance);
    }
  }
}