java - Implementing Runnable vs. extending Thread

Why is implementing Runnable a better option than extending from Thread class?

Answer

This way you decouple the computation (the what) from the execution (the when and/or the how).

With Runnable or Callable, you can for instance submit many work/computation to an Executor which will take care to schedule the stuffs. Here is an excerpt form ExecutorService:

pool = Executors.newFixedThreadPool(poolSize);
...

pool.execute(new Handler(serverSocket.accept()));
...
class Handler implements Runnable {
    ...
 }

Using Runnable/Callable gives you more flexibility that using Threads directly.