JavaFX PieChart InstantiationException

Question

我正在编写一个小程序，它读取一个txt文件并生成一个饼图。我正在使用JavaFX来做到这一点。它适用于所有代码都在同一个类中，但是当我尝试使用2个类并使用构造函数来调用它时，我得到一个InstantiationException。

驱动：

const id = {
_high: 0,
_low: 256,
remainder: { _low: 0, high: 0, remainder: null },
valueOf: function(){
return {}; /* valueOf fails to provide a primitive */
},
toString: function() {
return {}; /* toString fails to provide a primitive as well */
}
};


console.log(id + 10); // a "TypeError" is thrown :(

主类：

import java.util.ArrayList;
import java.util.List;

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.scene.chart.*;
import javafx.scene.Group;
import javafx.scene.control.Label;
import javafx.scene.input.MouseEvent;

public abstract class SeqDiagDriver extends Application {

    public static void main(String[] args) {

        launch(args);

    }

    @Override public void start(Stage stage) {

        sdPieChart sd = new sdPieChart("seqDiag/test1.txt");

        Scene scene = new Scene(new Group());
        stage.setTitle("Sequence Diagram");
        stage.setWidth(500);
        stage.setHeight(500);

        //Create new List that stores Name of objects and Number of outgoing messages
        List<PieChart.Data> seqData = new ArrayList<PieChart.Data>();

        for(int i = 0; i < sd.getNumObj(); i++){
            String[] objName = sd.getNameArr();
            int[] objOut = sd.getOutArr();
            seqData.add(new PieChart.Data(objName[i], objOut[i]));
        }

        //Adding the list with information to an ObservableList
        ObservableList<PieChart.Data> pieChartData = FXCollections.observableArrayList(seqData);

        final PieChart chart = new PieChart(pieChartData);
        chart.setTitle("Sequence Diagram");

        ((Group) scene.getRoot()).getChildren().add(chart);
        stage.setScene(scene);
        stage.show();
    }

}

这是产生的错误：

import java.io.*;
import java.util.List;
import java.util.ArrayList;

//Reads a txt file, gathers information needed, creates a pie chart with that information
public class sdPieChart {

    private String nameArr[];
    private int outArr[];
    private int numObjects = 0;

    sdPieChart(){    
    }

    sdPieChart(String in){
        readFile(in);
    }

    public void readFile(String inFile){
        BufferedReader br = null;

        List<String> nameObjects = new ArrayList<String>();
        List<Integer> numOut = new ArrayList<Integer>();

        try {
            //File from sequence Diagram containing information
            br = new BufferedReader(new FileReader(inFile));
            String str;

            //read lines and put inforamtion into 3 different Lists
            while((str = br.readLine()) != null){
                String tempName = str.substring(0, str.indexOf(":"));
                nameObjects.add(tempName);

                String out = str.substring(str.indexOf(":"), str.indexOf(","));
                String tempOut = out.substring(1);
                numOut.add(Integer.parseInt(tempOut));

            }

            //Convert lists to arrays
            nameArr = nameObjects.toArray(new String[0]);
            outArr = toIntArray(numOut);

            numObjects = nameArr.length;

        }

        catch (IOException e){
            e.printStackTrace();
        }
        finally{
            try {
                br.close();
            }
            catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    //Used to create int array
    static int[] toIntArray(List<Integer> list){
        int[] ret = new int[list.size()];
        for(int i = 0;i < ret.length;i++){
            ret[i] = list.get(i);
        }
        return ret;
    }

    public String[] getNameArr() {
        return nameArr;
    }

    public int[] getOutArr() {
        return outArr;
    }

    public int getNumObj() {
        return numObjects;
    }

    public void setNameArr(String[] nameArr) {
        this.nameArr = nameArr;
    }

    public void setOutArr(int[] outArr) {
        this.outArr = outArr;
    }

    public void setNumObjects(int numObjects)  {
        this.numObjects = numObjects;
    }
}

就像我说的，如果这一切都在一个类中，那么它工作正常，但我需要这样做，以便我能够在几个不同的类中调用它，允许我在多个类中创建饼图。