[Ch15] Adding Runnable example with Executor

package ch15;

import java.util.concurrent.Executor;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

public class MyRunnable implements Runnable {

   public void run() {

   }

}

class ExecutorTester {

   public static void main (String[] args) {

      Runnable threadJob = new MyRunnable();

      ExecutorService executor = Executors.newSingleThreadExecutor();

      executor.execute(threadJob);

      System.out.println(Thread.currentThread().getName() + ": back in main");

      Thread.dumpStack();

      executor.shutdown();

   }

}

class StackUtils {

   static String getCurrentStack() {

      StringBuffer stack = new StringBuffer();