code: public ThreadFactoryBuilder setPriority(int priority) {
      // Thread#setPriority() already checks for validity. These error messages
      // are nicer though and will fail-fast.
      checkArgument(
          priority >= Thread.MIN_PRIORITY,
          "Thread priority (%s) must be >= %s",
          priority,
          Thread.MIN_PRIORITY);
      checkArgument(
          priority <= Thread.MAX_PRIORITY,
          "Thread priority (%s) must be <= %s",
          priority,
          Thread.MAX_PRIORITY);
      this.priority = priority;
      return this;
    }
docs: Sets the priority for new threads created with this ThreadFactory.
  
  @param priority the priority for new Threads created with this ThreadFactory
  @return this for the builder pattern