code: public void setHistogramLevels(int[] levels) {
  		checkArgument(levels.length > 0, "levels amount must be at least 1");
  		for (int i = 1; i < levels.length; i++) {
  			checkArgument(levels[i] > levels[i - 1], "levels must be ascending");
  		}
  
  		histogramLevels = levels;
  		histogramValues = new long[levels.length + 1];
  	}
docs: endregion