ArffLoader loader = new ArffLoader();
    loader.setFile(new File("valid file"));
   Instances structure = loader.getStructure();
    structure.setClassIndex(1);

// train NaiveBayes
NaiveBayesMultinomialUpdateable n = new NaiveBayesMultinomialUpdateable();
FilteredClassifier f = new FilteredClassifier();
StringToWordVector s = new StringToWordVector();

f.setFilter(s);
f.setClassifier(n);
 f.buildClassifier(structure);
Instance current;
while ((current = loader.getNextInstance(structure)) != null)
  n.updateClassifier(current);

Evaluation eval = new Evaluation(structure);
 eval.crossValidateModel(f, structure, 10, new Random(1));
 System.out.println(eval.toSummaryString("nResultsn======n", false));




// output generated model
System.out.println(f);

NaiveBayesMultinomialUpdateable n = new NaiveBayesMultinomialUpdateable();
FilteredClassifier f = new FilteredClassifier();
StringToWordVector s = new StringToWordVector();

f.setFilter(s);
f.setClassifier(n);
 f.buildClassifier(structure);
Instance current;
while ((current = loader.getNextInstance(structure)) != null)
  n.updateClassifier(current);