TextArea的内容未填充

Question

我正在尝试向TextArea输出我文件中读取的内容。我能够打开JFileChooser，但是，我的程序无法完成将数组中的输出写入TextArea。提前谢谢！

public class GUI extends JFrame implements ActionListener{

ArrayList<Student> students = new ArrayList<Student>();
private JButton openFile;
private TextArea display;

public GUI(){
    super("Student Directory");
    setLayout(new FlowLayout());
    openFile = new JButton("Open File");
    openFile.addActionListener(this);
    add(openFile);
    display = new TextArea();
    add(display);
}


public void displayStudents(String[] output){
    display.setEditable(false);
    for(int i = 0; i<output.length; i++){
        display.append(output[i]+"\n");

    }
}

public void actionPerformed(ActionEvent e){
    if(e.getSource() == openFile){
        final JFileChooser jFileChooser = new JFileChooser();
        int returnVal = jFileChooser.showOpenDialog(this);
        if(returnVal == jFileChooser.APPROVE_OPTION){
            File file = jFileChooser.getSelectedFile();
            readFile(file);
        }
    }
}
private void readFile(File file) {
    int currentStudent = 0;

    Scanner input;
    try {
        input = new Scanner(new FileReader(file));
        while (input.hasNextLine()) {

            String line = input.nextLine();
            StringTokenizer st = new StringTokenizer(line, ",");

            while (st.hasMoreTokens()) {
                String first, last, idNo;
                last = st.nextToken();
                first = st.nextToken();
                idNo = st.nextToken();
                Student s = new Student(last, first, idNo);
                students.add(s);
                line = input.nextLine();
                st = new StringTokenizer(line, ",");
                while (st.hasMoreTokens()) {
                    String x = st.nextToken();
                    if (x.equals("-999")) {
                        line = input.nextLine();
                        st = new StringTokenizer(line, ",");
                        Float totalCredits = Float.parseFloat(st.nextToken());
                        Float gpa = Float.parseFloat(st.nextToken());
                        students.get(currentStudent).storeGPA(totalCredits, gpa);
                        currentStudent++;
                    } else {
                        String courseID = x;
                        float credits = Float.parseFloat(st.nextToken());
                        String grade = st.nextToken();
                        CourseList cl = new CourseList(courseID, grade, credits);
                        s.setCourses(cl);
                        line = input.nextLine();
                        st = new StringTokenizer(line, ",");
                    }
                }
            }

        }

        input.close();
        currentStudent = 0;

    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}
}

public class StudentDir {
static ArrayList<Student> students = new ArrayList<Student>();
static GUI newGUI;


public static void main(String args[]) throws IOException {

    GUI newGUI = new GUI();
    newGUI.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    newGUI.setSize(275,180);
    newGUI.setVisible(true);

    String[] unsorted = sortedArray.makeArray(students);
    String[] sorted = sortedArray.insertionSort(unsorted);
    newGUI.displayStudents(unsorted);
    newGUI.displayStudents(sorted);
    for(int i = 0; i < unsorted.length;i++){
        System.out.println(unsorted[i]+" | "+sorted[i]);
    }
}
}