code: private double getPrior(int classIndex) {
  		// Maximum likelihood
  		Double currentCount = this.classInstances.get(classIndex);
  		if (currentCount == null || currentCount == 0)
  			return 0;
  		else
  			return currentCount * 1. / this.instancesSeen;
  	}
docs: Compute the prior for the given classIndex.
  
  Implemented by maximum likelihood at the moment.
  
  @param classIndex
  Id of the class for which we want to compute the prior.
  @return Prior probability for the requested class