Question

我正在尝试使用Java从保存在sql数据库中的数据生成统计图（BarCharts和LineCharts）。该数据可能会不时更改。

我尝试使用ObservableLists，但收到错误消息。

以下是我到目前为止尝试过的内容；注意：这位于DatabaseHandler类中

public ObservableList<BarChart.Data> getItemGraphStatistics(){
        ObservableList<BarChart.Data> data = FXCollections.observableArrayList();

        String sql = "SELECT itemID, COUNT(*) FROM (SELECT itemID FROM SALES UNION ALL SELECT itemID FROM STOCK) t GROUP BY itemID";
        System.out.println(sql );
        ResultSet rs = handler.execQuery(sql);
        try{

            while(rs.next()){
                String item= rs.getString("itemID");
                int count = rs.getInt(2);

                data.add(new BarChart.Data(item+ "(" + count + ")", count));

            }
        } catch (SQLException ex) {
            Logger.getLogger(DatabaseHandler.class.getName()).log(Level.SEVERE, null, ex);
        }
        return data;

    }

运行上述代码时

java.lang.ClassCastException: javafx.scene.chart.XYChart$Data cannot be cast to javafx.scene.chart.XYChart$Series

当我尝试将BarChart.Data更改为BarChart.Series时，无法将int转换为observableList错误消息。

以下是上述示例的示例；

import com.jfoenix.controls.JFXButton;
import com.jfoenix.controls.JFXRadioButton;
import com.jfoenix.controls.JFXTextField;
import java.net.URL;
import java.util.Calendar;
import java.util.Dictionary;
import java.util.Hashtable;
import java.util.ResourceBundle;
import java.util.concurrent.TimeUnit;
import javafx.event.ActionEvent;
import javafx.event.Event;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.chart.BarChart;
import javafx.scene.chart.CategoryAxis;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.PieChart;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.DatePicker;
import javafx.scene.control.ToggleGroup;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.HBox;
import sales.manager.database.DatabaseHandler;

/**
 * FXML Controller class
 *
 * @author Garande
 */
public class PerformanceAnalyzerController implements Initializable {

    @FXML
    private AnchorPane analysisHandler;
    @FXML
    private AnchorPane graphHandler;
    @FXML
    private PieChart piechart;
    @FXML
    private BarChart<?, ?> barchart;
    @FXML
    private LineChart<?, ?> linechart;

    @FXML
    private NumberAxis yBarGraph;
    @FXML
    private CategoryAxis xBarGraph;
    @FXML
    private NumberAxis yLineGraph;
    @FXML
    private CategoryAxis xLineGraph;

    DatabaseHandler handler = DatabaseHandler.getInstance();

    /**
     * Initializes the controller class.
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {


    }    

    @FXML
    private void performAnalysisOperation(ActionEvent event) {
        //Performing analysis operation

        barchart.setData(handler.getItemGraphStatistics());
        graphHandler.getChildren().add(barchart);
    }
}

Answer 1

data的{{1}}属性包含一个XYChart。每个ObservableList<XYChart.Series> 还都有一个XYChart.Series属性，但它拥有一个data。问题是您的方法返回了一个ObservableList<XYChart.Data>，然后您尝试在ObservableList<XYChart.Data>上进行设置-类型不匹配。我不确定您如何获得XYChart.data，因为您的代码甚至都不会编译。

您需要将数据列表包装在系列中，然后将系列添加到图表中。您还应该avoid using raw types。 ClassCastException和Series都具有类型参数，但您未指定它们。根据您构建Data的方式，您的代码应类似于（为简洁起见，省略了一些代码）：

Data

并且：

public class PerformanceAnalyzerController {

    @FXML private BarChart<String, Number> barChart;

    @FXML
    private void performAnalysisOperation(ActionEvent event) {
        //Performing analysis operation

        ObservableList<XYChart.Data<String, Number>> data = handler.getItemsGraphicsStatisitics();
        XYChart.Series<String, Number> series = new XYChart.Series<>("Series Name", data);

        barchart.getData().setAll(series);
        graphHandler.getChildren().add(barchart);
    }

}

注意：我将// Use generic types public ObservableList<XYChart.Data<String, Number>> getItemGraphStatistics(){ ObservableList<XYChart.Data<String, Number>> data = FXCollections.observableArrayList(); String sql = "SELECT itemID, COUNT(*) FROM (SELECT itemID FROM SALES UNION ALL SELECT itemID FROM STOCK) t GROUP BY itemID"; System.out.println(sql ); ResultSet rs = handler.execQuery(sql); try{ while(rs.next()){ String item= rs.getString("itemID"); int count = rs.getInt(2); // add diamond operator "<>" data.add(new XYChart.Data<>(item+ "(" + count + ")", count)); } } catch (SQLException ex) { Logger.getLogger(DatabaseHandler.class.getName()).log(Level.SEVERE, null, ex); } return data; }的使用替换为BarChart.Data，但在这种情况下我认为这并不重要。

如何使用ObservableLists在Javafx中创建BarChart或LineChart

1 个答案: