code: public int add(T item) {
  		
  		Integer count = map.get(item);
  		
  		if(count == null) {
  			map.put(item, 1);
  			return 1;
  		} else {
  			map.put(item, count + 1);
  			return count + 1;
  		}
  	}
docs: add item to histogram, increasing its frequency by one