JAVA proqramlaşdırmada comboBox silinmə

Salam,
JAVA proqramlaşdırma dilini yaxşı bilən şəxslərin köməyinə ehtiyacım var. Bir proqram üzərində çalışıram və bir nöqtədə yardım lazımdı. Kömək etmək istəyən olsa çox məmnun olaram.

Class-da mövcud kodlar bunlardır. Bu CLASS-ın etməli olduğu şey: mən fakulteti seçəndə o fakultetə bağlı kafedralar yüklənsin və sonra kafedra seçdikdə ona uyğun qruplar. Lakin problem odur ki, hər fakulteti seçəndə comboDepartment daxilindəki mövcud kafedralar silinməlidir və seçilən fakultetə uyğun kafedralar yüklənməlidir və də kafedra seçdikdə ona uyğun qruplar amma bu alınmır. Xəta alıram. Xətanı da qeyd edirəm aşağı… Bilirəm ki, problem comboDepartment.removeAllItems()-dən qaynaqlanır. Harda istifadə etməliyəm bu metodu və ya necə istifadə etməliyəm? Köməyi dəyənlər üçün indidən təşəkkürlər..

import java.awt.EventQueue;

import javax.swing.JFrame;

import java.awt.BorderLayout;
import java.io.BufferedReader;
import java.io.FileReader;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;

import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JComboBox;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.ListSelectionModel;

import net.miginfocom.swing.MigLayout;

import javax.swing.UIManager;
import javax.swing.border.LineBorder;
import javax.swing.table.DefaultTableModel;
import javax.swing.JPopupMenu;

import java.awt.Component;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JMenuItem;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;


public class showStudentSection {

    private String db;
    private String db_user;
    private String db_pass;

    private JFrame frmStudents;
    private JTable table;

    private Lang lang = new Lang();
    private Theme theme = new Theme();
    private doSpecificOperations ops = new doSpecificOperations();
    private getTables getTable = new getTables();

    private JComboBox<String> comboGroup;
    private JComboBox<String> comboDepartment;
    private JComboBox<String> comboFaculty;
    private ArrayList<Integer> groupID = new ArrayList<Integer>();
    private ArrayList<Integer> depID = new ArrayList<Integer>();
    private ArrayList<Integer> facultyID = new ArrayList<Integer>();

    private Boolean first_time_fac = true;
    private Boolean first_time_dep = true;
    private Boolean first_time_grp = true;

    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel("javax.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch (Throwable e) {
            e.printStackTrace();
        }
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    showStudentSection window = new showStudentSection();
                    window.frmStudents.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }


    public showStudentSection() {
        initialize();
    }


    private void initialize() {
        getDB();

        frmStudents = new JFrame();
        frmStudents.getContentPane().setBackground(theme.setColor(1));
        frmStudents.setTitle("Students");
        frmStudents.setBounds(100, 100, 909, 473);
        frmStudents.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frmStudents.getContentPane().setLayout(new BorderLayout(0, 0));

        JPanel upPanel = new JPanel();
        upPanel.setBorder(new LineBorder(theme.setColor(3)));
        upPanel.setBackground(theme.setColor(1));
        frmStudents.getContentPane().add(upPanel, BorderLayout.NORTH);

        JLabel lblFaculty = new JLabel("Faculty:");
        lblFaculty.setBackground(theme.setColor(1));
        lblFaculty.setForeground(theme.setColor(2));
        upPanel.add(lblFaculty);

        comboFaculty = new JComboBox<String>();
        comboFaculty.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                if(first_time_fac==false){
                    LoadDepartments(facultyID.get(comboFaculty.getSelectedIndex()));

                }

                first_time_fac=false;
            }
        });
        comboFaculty.setBackground(theme.setColor(1));
        upPanel.add(comboFaculty);

        JLabel lblDepartment = new JLabel("Department:");
        lblDepartment.setBackground(theme.setColor(1));
        lblDepartment.setForeground(theme.setColor(2));
        upPanel.add(lblDepartment);

        comboDepartment = new JComboBox<String>();
        comboDepartment.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                if(first_time_dep==false){
                    LoadGroups(depID.get(comboDepartment.getSelectedIndex()));
                }

                first_time_dep=false;
            }
        });
        comboDepartment.setBackground(theme.setColor(1));
        upPanel.add(comboDepartment);

        JLabel lblGroup = new JLabel("Group:");
        lblGroup.setBackground(theme.setColor(1));
        lblGroup.setForeground(theme.setColor(2));
        upPanel.add(lblGroup);

        comboGroup = new JComboBox<String>();
        comboGroup.setBackground(theme.setColor(1));
        upPanel.add(comboGroup);

        JPanel downPanel = new JPanel();
        downPanel.setBorder(new LineBorder(theme.setColor(3)));
        downPanel.setBackground(theme.setColor(1));
        frmStudents.getContentPane().add(downPanel, BorderLayout.SOUTH);

        JButton btnClose = new JButton("Close");
        btnClose.setBackground(theme.setColor(1));
        btnClose.setForeground(theme.setColor(2));
        downPanel.add(btnClose);

        JPanel leftPanel = new JPanel();
        leftPanel.setBackground(theme.setColor(1));
        frmStudents.getContentPane().add(leftPanel, BorderLayout.WEST);
        leftPanel.setLayout(new MigLayout("", "[]", "[][][][][][][]"));

        JLabel lblStudentOperations = new JLabel("Student operations");
        lblStudentOperations.setBackground(theme.setColor(1));
        lblStudentOperations.setForeground(theme.setColor(2));
        leftPanel.add(lblStudentOperations, "cell 0 0,growx");

        JButton btnAddStudent = new JButton("Add student");
        btnAddStudent.setBackground(theme.setColor(1));
        btnAddStudent.setForeground(theme.setColor(2));
        leftPanel.add(btnAddStudent, "cell 0 1,growx");

        JButton btnDeleteStudent = new JButton("Delete student");
        btnDeleteStudent.setBackground(theme.setColor(1));
        btnDeleteStudent.setForeground(theme.setColor(2));
        leftPanel.add(btnDeleteStudent, "cell 0 2,growx");

        JButton btnEditStudent = new JButton("Edit student");
        btnEditStudent.setBackground(theme.setColor(1));
        btnEditStudent.setForeground(theme.setColor(2));
        leftPanel.add(btnEditStudent, "cell 0 3,growx");

        JLabel lblOperations = new JLabel("Other operations");
        lblOperations.setBackground(theme.setColor(1));
        lblOperations.setForeground(theme.setColor(2));
        leftPanel.add(lblOperations, "cell 0 4,growx");

        JButton btnFindStudent = new JButton("Find student");
        btnFindStudent.setBackground(theme.setColor(1));
        btnFindStudent.setForeground(theme.setColor(2));
        leftPanel.add(btnFindStudent, "cell 0 5,growx");

        JButton btnSaveTable = new JButton("Save table (xls)");
        btnSaveTable.setBackground(theme.setColor(1));
        btnSaveTable.setForeground(theme.setColor(2));
        leftPanel.add(btnSaveTable, "cell 0 6,growx");

        JPanel center = new JPanel();
        frmStudents.getContentPane().add(center, BorderLayout.CENTER);
        center.setLayout(new BorderLayout(0, 0));

        JScrollPane scrollPane = new JScrollPane();
        center.add(scrollPane, BorderLayout.CENTER);

        table = new JTable();
        table.setSelectionBackground(theme.setColor(5));
        table.setShowVerticalLines(true);
        table.setShowHorizontalLines(true);
        table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        scrollPane.setViewportView(table);

        JPopupMenu popupMenu = new JPopupMenu();
        addPopup(table, popupMenu);

        JMenuItem mntmSeeStudentInformation = new JMenuItem("See student information");
        popupMenu.add(mntmSeeStudentInformation);

        LoadFaculties();
        LoadDepartments(facultyID.get(comboFaculty.getSelectedIndex()));
        LoadGroups(depID.get(comboDepartment.getSelectedIndex()));

        LoadStudents("WHERE facultyID="+facultyID.get(comboFaculty.getSelectedIndex())+" AND depID="+depID.get(comboDepartment.getSelectedIndex()) + " AND groupID="+groupID.get(comboGroup.getSelectedIndex()));

    }

    private void LoadStudents(String query)
    {

        DefaultTableModel model = new DefaultTableModel(){

            private static final long serialVersionUID = 1L;

            @Override
            public boolean isCellEditable(int row, int column)
            {
                return false;
            }

        };
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection elaqe = DriverManager.getConnection(db,db_user,db_pass);
            Statement sorgu = elaqe.createStatement();
            ResultSet netice = sorgu.executeQuery("SELECT * FROM students " + query);
            int c_count = netice.getMetaData().getColumnCount();

            model.addColumn(lang.translate("student_no"));
            model.addColumn(lang.translate("name_surname"));
            model.addColumn(lang.translate("sex"));
            model.addColumn(lang.translate("birthday"));
            model.addColumn(lang.translate("birth_place"));
            model.addColumn(lang.translate("admission_year"));
            model.addColumn(lang.translate("profession"));
            model.addColumn(lang.translate("phone"));
            model.addColumn(lang.translate("e_mail"));
            model.addColumn(lang.translate("education_status"));

            while(netice.next())
            {
                Object[] row = new Object[c_count];
                row[0] = netice.getString("studentNO");
                row[1] = netice.getString("name");
                row[2] = netice.getString("gender");
                row[3] = netice.getString("date_birth");
                row[4] = netice.getString("place_birth");
                row[5] = netice.getString("admission_date");
                row[6] = getTable.getStudentProfessionText(netice.getString("profession"));
                row[7] = netice.getString("phone");
                row[8] = netice.getString("e_mail");
                row[9] = getTable.getStudentStatusText(netice.getString("education_status"));

                model.addRow(row);
            }

            elaqe.close();
            sorgu.close();

            table.setModel(model);
        } catch (Exception e) {
            ops.createInfoMessage(lang.translate("error"),lang.translate("db_error")+" (" + e.toString().substring(0, 40) + ")");
        }
    }

    private void LoadFaculties()
    {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection elaqe = DriverManager.getConnection(db,db_user,db_pass);
            Statement sorgu = elaqe.createStatement();
            ResultSet netice = sorgu.executeQuery("SELECT * FROM faculties");

            while(netice.next())
            {
                comboFaculty.addItem(netice.getString("name"));
                facultyID.add(netice.getInt("facultyID"));
            }

            elaqe.close();
            sorgu.close();
        } catch (Exception e) {
            ops.createInfoMessage(lang.translate("error"),lang.translate("db_error")+" (" + e.toString().substring(0, 40) + ")");
        }
    }

    private void LoadDepartments(int facultyID)
    {       
        comboDepartment.removeAllItems();
        depID.clear();
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection elaqe = DriverManager.getConnection(db,db_user,db_pass);
            Statement sorgu = elaqe.createStatement();
            ResultSet netice = sorgu.executeQuery("SELECT * FROM department WHERE facultyID="+facultyID);

            while(netice.next())
            {
                comboDepartment.addItem(netice.getString("name"));
                depID.add(netice.getInt("depID"));
            }

            elaqe.close();
            sorgu.close();
        } catch (Exception e) {
            ops.createInfoMessage(lang.translate("error"),lang.translate("db_error")+" (" + e.toString().substring(0, 40) + ")");
        }
    }

    private void LoadGroups(int depID)
    {   
        comboGroup.removeAllItems();
        groupID.clear();
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection elaqe = DriverManager.getConnection(db,db_user,db_pass);
            Statement sorgu = elaqe.createStatement();
            ResultSet netice = sorgu.executeQuery("SELECT * FROM groups WHERE depID="+depID);

            while(netice.next())
            {
                comboGroup.addItem(netice.getString("name"));
                groupID.add(netice.getInt("groupID"));
            }

            elaqe.close();
            sorgu.close();
        } catch (Exception e) {
            ops.createInfoMessage(lang.translate("error"),lang.translate("db_error")+" (" + e.toString().substring(0, 40) + ")");
        }
    }

    private void getDB()
    {
        try {
            BufferedReader bf = new BufferedReader(new FileReader(".\\mysql.db"));
            db = ops.decodeText(bf.readLine());
            db_user = ops.decodeText(bf.readLine());
            db_pass = ops.decodeText(bf.readLine());

            bf.close();
        } catch (Exception e) {
            ops.createInfoMessage(lang.translate("error"),lang.translate("cant_get_db_info")+" (" + e.toString().substring(0, 40) + ")");
        }
    }

    private static void addPopup(Component component, final JPopupMenu popup) {
        component.addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    showMenu(e);
                }
            }
            public void mouseReleased(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    showMenu(e);
                }
            }
            private void showMenu(MouseEvent e) {
                popup.show(e.getComponent(), e.getX(), e.getY());
            }
        });
    }
}

Exception in thread "AWT-EventQueue-0"  java.lang.ArrayIndexOutOfBoundsException: -1
at java.util.ArrayList.elementData(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at showStudentSection$3.actionPerformed(showStudentSection.java:133)
at javax.swing.JComboBox.fireActionEvent(Unknown Source)
at javax.swing.JComboBox.contentsChanged(Unknown Source)
at javax.swing.JComboBox.intervalRemoved(Unknown Source)
at javax.swing.AbstractListModel.fireIntervalRemoved(Unknown Source)
at javax.swing.DefaultComboBoxModel.removeAllElements(Unknown Source)
at javax.swing.JComboBox.removeAllItems(Unknown Source)
at showStudentSection.LoadDepartments(showStudentSection.java:310)
at showStudentSection.access$4(showStudentSection.java:308)
at showStudentSection$2.actionPerformed(showStudentSection.java:112)
at javax.swing.JComboBox.fireActionEvent(Unknown Source)
at javax.swing.JComboBox.setSelectedItem(Unknown Source)
at javax.swing.JComboBox.setSelectedIndex(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup$Handler.mouseReleased(Unknown Source)
at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup$1.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$400(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)**strong text**