Cool Runnables

A frequent reason to implement Runnable is, a class already extends other class we want it's objects to be active objects.

Another important reason is runnable can be used as a generic call back.
We can have a method like below doCallback where it calls back run on given runnable.

  doCallback(Runnable r){
    ...;
    r.run();
    ...
  }

This idiom is used in SwingUtilities.invokeLater(Runnable r), and SwingUtilitie.invokeAndWait(r). In these runnable is posted to a event queue and AWTEvent thread reads it and calls run from event thread. This makes given runnable called execute in a particular thread.

Recently I have been using this idiom in our persistence framework, we do normal operations on our business objects and post persistence tasks to a set of database aware threads. These db aware threads call our runnable task and do pre/post processing(transaction, connection management etc). Isn't it cool?