code: public synchronized void setPoolSize(int poolSize)
      {
          if (poolSize < 0)
          {
              throw new IllegalArgumentException("New poolSize (" + poolSize + ") is must not be negative");
          }
  
          if (pool != null)
          {
              pool.setCorePoolSize(poolSize);
          }
          this.poolSize = poolSize;
      }
docs: Sets the default number of worker threads in the thread pool. <br>
  This is the number of threads that are available even if they are idle.
  <br>
  The default pool size is 10.
  
  @param poolSize the size of the worker thread pool.
  @throws IllegalArgumentException if the new pool size is negative
  @see java.util.concurrent.ThreadPoolExecutor#setCorePoolSize(int)