Preconditions.checkArgument(dataModel != null, "dataModel is null");
Preconditions.checkArgument(samplingRate > 0.0 && samplingRate <= 1.0, "samplingRate must be in (0,1]");
this.userSimilarity = userSimilarity;
this.dataModel = dataModel;
this.samplingRate = samplingRate;
this.refreshHelper = new RefreshHelper(null);
this.refreshHelper.addDependency(this.dataModel);
this.refreshHelper.addDependency(this.userSimilarity);
}