code: public void setCooldownExpirationByTriggerAndMetric(Trigger trigger, Metric metric, long cooldownExpiration) {
          requireArgument(cooldownExpiration >= 0, "Cool down expiration time cannot be negative.");
  
  		String key = _hashTriggerAndMetric(trigger, metric);
  		this.cooldownExpirationByTriggerAndMetric.put(key, cooldownExpiration);
      }
docs: Sets the cool down expiration time of the notification given a metric,trigger combination.
  
  @param trigger   The trigger
  @param metric    The metric
  @param  cooldownExpiration  cool down expiration time in milliseconds