posted 11 years ago
I believe you're asking why you might want to pass a Runnable instance to Thread's constructor instead of simply extending the Thread class. A compelling reason is given in Core Java 2: Volume II - Advanced Features by Cay S. Horstmann and Gary Cornell...
...forming a subclass of the Thread class ... is no longer recommended. You should decouple the task that is to be run in parallel from the mechanism of running it.