Java -WEKA：对单个实例进行分类总是得到0

Question

我在WEKA中对单个实例进行分类存在问题，这是我的代码：

public void addInstance() throws Exception {
    Scanner s = new Scanner(System.in);
    DenseInstance newInstance  = new DenseInstance(m_Training.numAttributes());
    for(int i = 0 ; i < m_Training.numAttributes()-1 ; i++)
    {
       double value = s.nextDouble();
       newInstance.setValue(i , value);
       //i is the index of attribute
       //value is the value that you want to set
    }
    newInstance.setValue(m_Training.numAttributes()-1, Float.NaN);
    //add the new instance to the main dataset at the last position
    m_Training.add(newInstance);

    // Print header and instances. 
    System.out.println("\nDataset:\n"); 
    System.out.println(m_Training);

    System.out.print("\n\nClassification result : ");
    System.out.println(m_Classifier.classifyInstance(m_Training.instance(150)));
    System.out.println(m_Training.instance(150));
    System.out.println(m_Training.classAttribute().value((int)m_Classifier.classifyInstance(m_Training.instance(150))));
}

但它总是给出0.0的结果。我已经阅读了这个教程：weka: how to get class name from testing single instance但是，程序只给了我0.0，类名总是“iris-setosa”。

我在这个程序中使用了Iris.arff，而分类器（m_classifier）是J48。我不知道为什么它不起作用，任何帮助赞赏