fc.setClassifier(j48);
// train using stock_training_data.arff:
fc.buildClassifier(training_data);
// test using stock_testing_data.arff:
for (int i = 0; i < testing_data.numInstances(); i++) {
double pred = fc.classifyInstance(testing_data.instance(i));
System.out.print("given value: " + testing_data.classAttribute().value((int)testing_data.instance(i).classValue()));
System.out.println(". predicted value: " + testing_data.classAttribute().value((int) pred));
}
}