错误在Java代码中使用WEKA API：Class Attribute Not Set？

我试图在我的 java代码中使用weka API.我使用J48树分类在 MySQL数据库中分类我的数据集,但是我有这个错误：

Trying to add database driver (JDBC): RmiJdbc.RJDriver - Error,not in CLAsspATH?
Trying to add database driver (JDBC): jdbc.idbDriver - Error,not in CLAsspATH?
Trying to add database driver (JDBC): com.mckoi.JDBCDriver - Error,not in CLAsspATH?
Trying to add database driver (JDBC): org.hsqldb.jdbcDriver - Error,not in CLAsspATH?
weka.core.UnassignedClassException: weka.classifiers.trees.j48.C45PruneableClassifierTree: Class attribute not set!
        at weka.core.Capabilities.test(Capabilities.java:1086)
        at weka.core.Capabilities.test(Capabilities.java:1018)
        at weka.core.Capabilities.testWithFail(Capabilities.java:1297)
.....

这是我的代码：

try{
       DatabaseLoader loader = new DatabaseLoader();
      loader.setSource("jdbc:MysqL://localhost:3306/cuaca","root","491754");
       loader.setQuery("select * from data_training");
      Instances data = loader.getDataSet();

        jTextArea1.append(data.toString());

        String[] options = new String[1];
        options[0] = "U"; // unpruned tree
        J48 tree = new J48(); // new instance of tree
       tree.setoptions(options); // set the option
       tree.buildClassifier(data); // build classifier
       //Evaluation eval=new Evaluation(data);
       //eval.crossValidateModel(tree,data,10,new Random(1));
       //jTextArea1.append(eval.toSummaryString("\n HASILNYA \n",false));

 }catch(IOException ioe){ioe.printstacktrace();}
        catch(Exception e){e.printstacktrace();}

数据集实际上出现在textarea中：

@relation data_training

@attribute Tmean numeric
@attribute Tmax numeric
@attribute Td numeric
@attribute RH numeric
@attribute SLP numeric
@attribute STP numeric
@attribute Wind_ave numeric
@attribute Wind_max numeric
@attribute Hujan {Y,T}

@data
25.9,31.6,23.1,93.4,1008.5,998.2,2.6,12.9,Y
27.6,31.4,22.3,87,1009.6,999.3,0.8,3.1,T
27.4,32.6,21.9,86.1,1009.4,999.2,4.5,14.3,T
27.6,32.2,22.4,87.3,1009.1,998.9,2.4,8.2,T

我会知道为什么错误出现(Class Attribute Not Set !!)

解决方法

在将数据集传入分类器之前,您应该设置类索引.您的分类器必须知道哪个是您的结果变量.
这些行后

loader.setQuery("select * from data_training");
Instances data = loader.getDataSet();

添加以下内容：

data.setClassIndex(data.numAttributes() - 1);

如果Hujan是你的类属性(结果变量)

见Api Docs for more Info