Прослушивание кнопок в Java AWT

import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
 
 
class But extends Button implements ActionListener{
    Color cr = Color.red;
    Color cw = Color.white;
    Color cb = Color.black;
    But(String label){
        super(label);
        setSize(10,10);
        setBackground(cw);
        setForeground(cb);
        addActionListener(this);
    }
    public void actionPerformed(ActionEvent ae){
        if(getLabel().equals("  "))return;
        if(getBackground().equals(cr)){
            setBackground(cw);
            setForeground(cb);
        }
        else{
            setBackground(cr);
            setForeground(cw);
        }
    }
}
 
class EmptyCheckboxPan extends Panel{
    CheckBoxPane cbp = new CheckBoxPane();
    EmptyCheckboxPan(){
        setLayout(null);
        setSize(95, 285);
        setBackground(Color.darkGray);
        setLocation(5, 5);
        setVisible(true);
        add(cbp);
    }
    CheckBoxPane getCheckBoxPane(){
        return cbp;
    }
}
 
class CheckBoxPane extends Panel{
    Checkbox[] cb = new Checkbox[2];
    CheckboxGroup cbg = new CheckboxGroup();
    String[] label = {"Holidays ", "Working days "};
 
    CheckBoxPane(){
        setLayout(null);
        setSize(95, 285);
        setBackground(Color.darkGray);
        setLocation(0, 0);
        setVisible(true);
 
        for(int i = 0, k = 90; i < label.length; i++, k = k + 50){
            cb[i] = new Checkbox(label[i], cbg, false);
            cb[i].setBackground(Color.darkGray);
            cb[i].setForeground(Color.white);
            cb[i].setSize(90,50);
            cb[i].setLocation(3, k);
            add(cb[i]);
        }
    }
}
 
class EditButton extends Button implements ActionListener{
    //CheckBoxPane butpan;
    int b;
    Color cr = Color.red;
    CalendarPanel calpan;
    But[][] refBut;
    EditButton(But[][] b){
        super();
        refBut = b;
        //butpan = bp;
        setLabel("E d i t");
        setSize(50,30);
        setLocation(25,105);
        setBackground(Color.LIGHT_GRAY);
 
        //addActionListener(this);
        ActionListener actionlistener = new ButtonsListener();
        addActionListener(actionlistener);
    }
    public void actionPerformed(ActionEvent ae){
        //butpan.setVisible(true);
    }
    public class ButtonsListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //refBut = calpan.getBut();
            for(int i = 0; i < refBut.length; i++){
                for(int j = 0; j < 6; j++)
                    refBut[i][j].setEnabled(true);
            }
        }
   }
}
 
class OKButton extends Button implements ActionListener{
    CheckBoxPane bp;
    OKButton(CheckBoxPane bp){
        super();
        this.bp = bp;
        setLabel("O K");
        setLocation(25,150);
        setSize(50,30);
        setBackground(Color.LIGHT_GRAY);
        addActionListener(this);
    }
    public void actionPerformed(ActionEvent ae){
        //bp.setVisible(false);
    }
}
 
class ButtonsPane extends Panel{
    EditButton eb;
    OKButton okb;
    But[][] refBut = new But[7][6];
    ButtonsPane(EmptyCheckboxPan ecp){
        super();
        setLayout(null);
        setBackground(Color.darkGray);
        setSize(100, 285);
        setLocation(880, 5);
        eb = new EditButton(refBut);
        //eb = new EditButton(ecp.getCheckBoxPane());
        okb = new OKButton(ecp.getCheckBoxPane());
        add(eb);
        add(okb);
    }
}
 
class DaysPane{
    String[] name = {"Mon","Tue","Wed","Thu","Fri","Sat","Sun"};
    Panel p = new Panel();
    Button[] refBut = new Button[name.length];
    int setx, sety;
    DaysPane(int x, int y){
        super();
        setx = x;
        sety = y;
        p.setLayout(null);
        p.setBackground(Color.gray);
        p.setSize(50, 250);
        p.setLocation(setx, sety);
        for(int i = 0, k = 5; i < name.length; i++, k += 35){
            refBut[i] = new Button(name[i]);
            refBut[i].setSize(40,30);
            refBut[i].setLocation(5,k);
            refBut[i].setBackground(Color.white);
            p.add(refBut[i]);
        }
    }
    Panel getDaysPane(){
        return p;
    }
}
 
class DaysLabel{
    Label days = new Label("Days", Label.CENTER);
    int setx, sety;
    Font font = new Font("Verdana", Font.BOLD, 16);
    DaysLabel(int x, int y){
        super();
        setx = x;
        sety = y;
        days.setBackground(Color.gray);
        days.setFont(font);
        days.setLocation(setx, sety);
        days.setSize(new Dimension(50, 30));
    }
    Label getDaysLabel(){
        return days;
    }
}
 
class CalendarPanel{
    int col;
    int dayOfMonth = 0;
    int k = 0;
    int year;
    String monthName;
    But[][] b;
    JPanel pan = new JPanel();
    GregorianCalendar greg;
    CalendarPanel(JPanel p, int y, String month){
        super();
        pan = p;
        year = y;
        monthName = month;
 
        if(monthName == "September"){
            greg = new GregorianCalendar(year,8,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if(monthName == "October"){
            greg = new GregorianCalendar(year,9,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if(monthName == "November"){
            greg = new GregorianCalendar(year,10,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if(monthName == "December"){
            greg = new GregorianCalendar(year,11,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if(monthName == "January"){
            greg = new GregorianCalendar(year+1,0,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if(monthName == "February"){
            greg = new GregorianCalendar(year+1,1,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if(monthName == "March"){
            greg = new GregorianCalendar(year+1,2,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if(monthName == "April"){
            greg = new GregorianCalendar(year+1,3,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if(monthName == "May"){
            greg = new GregorianCalendar(year+1,4,1);
            k = greg.get(Calendar.DAY_OF_WEEK);
            dayOfMonth = greg.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
 
        //calendar, 31 days
        //dates
        int[] d = new int[dayOfMonth+1];
        for(int i = 1; i < d.length; i++)
            d[i] = i;
 
        //determine the day of the week in range 0-7
        if(k == 1)
            k = 6;
        else
            k -= 2;
 
        //formation of the blank calendar
        int col;
        col = k <= 4?5:6;
        b = new But[7][col];
        for(int i = 0; i < b.length; i++)
            for(int j = 0; j < col; j++)
                b[i][j] = new But("  ");
 
        //set the days of the week in the panel
        pan.setBackground(Color.gray);
        pan.setBorder(new EmptyBorder(5,5,5,5));
        pan.setLayout(new GridLayout(7,col+1,5,5));
        for(int i = 0; i < b.length; i++){
            for(int j = 0; j < col; j++){
                b[i][j].setEnabled(false);
                pan.add(b[i][j]);
            }
        }
 
        //create the calendar
        int n;
        n = 1;
        for(int j = 0; j < col; j++)
            for(int i = j == 0?k:0; (i < b.length) && (n < d.length); i++){
                b[i][j].setLabel("" + d[n++]);
            }
 
        //Mark the Saturdays and Sundays
        for(int i = 5; i < 7; i++)
            for(int j = 0; j < col; j++){
                if(b[i][j].getLabel().equals("  "))
                    b[i][j].setBackground(Color.lightGray);
                else{
                    b[i][j].setBackground(Color.red);
                    b[i][j].setForeground(Color.white);
                }
            }
    }
    JPanel getPanel(){
        return pan;
    }
    But[][] getBut(){
        return b;
    }
}
 
public class ColorButton {
 
    private static void createAndShowGUI(){
        CalendarPanel cp1;
        CalendarPanel cp2;
        Frame f = new Frame("Teacher's Calendar");
        f.setBackground(Color.lightGray);
        f.setSize(991,613);
        f.setResizable(false);
        f.setLayout(new GridLayout(2,1,5,5));
 
        //close the application
        f.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent we){
                System.exit(0);
            }
        });
 
        Panel TopPanel = new Panel();
        TopPanel.setBackground(Color.lightGray);
        TopPanel.setLayout(null);
        Panel BottomPanel = new Panel();
        BottomPanel.setBackground(Color.lightGray);
        BottomPanel.setLayout(null);
 
        f.add(TopPanel);
        f.add(BottomPanel);
 
        //add a empty darkgray panel
        EmptyCheckboxPan eckbp = new EmptyCheckboxPan();
        TopPanel.add(eckbp);
 
        //add a buttons panel
        ButtonsPane buttons = new ButtonsPane(eckbp);
        TopPanel.add(buttons);
 
        //add a days button top panel
        DaysPane topdays = new DaysPane(105,40);
        TopPanel.add(topdays.getDaysPane());
 
        //add a days button bottom panel
        DaysPane bottomdays = new DaysPane(5,35);
        BottomPanel.add(bottomdays.getDaysPane());
 
        //add a top label DAYS
        DaysLabel days = new DaysLabel(105, 5);
        TopPanel.add(days.getDaysLabel());
 
        //add a bottom label DAYS
        DaysLabel days1 = new DaysLabel(5, 0);
        BottomPanel.add(days1.getDaysLabel());
 
        String[] mName1 = {"September","October","November","December"};
        Label[] lab = new Label[mName1.length];
        Font font = new Font("Verdana", Font.BOLD, 16);
        for(int i = 0, k = 160; i < lab.length; i++, k = k + 180){
            lab[i] = new Label(mName1[i], Label.CENTER);
            lab[i].setBackground(Color.gray);
            lab[i].setFont(font);
            lab[i].setLocation(k, 5);
            lab[i].setSize(new Dimension(175, 30));
            TopPanel.add(lab[i]);
        }
 
        JPanel[] calendarPanel1 = new JPanel[4];
        for(int i = 0, k = 160; i < calendarPanel1.length; i++, k = k + 180){
            calendarPanel1[i] = new JPanel();
            cp1 = new CalendarPanel(calendarPanel1[i], 2015, mName1[i]);
            calendarPanel1[i] = cp1.getPanel();
            calendarPanel1[i].setLocation(k, 40);
            calendarPanel1[i].setSize(new Dimension(175, 250));
            TopPanel.add(calendarPanel1[i]);
        }
 
        String[] mName2 = {"January","February","March","April","May"};
        Label[] lab2 = new Label[mName2.length];
        for(int i = 0, k = 60; i < lab2.length; i++, k = k + 185){
            lab2[i] = new Label(mName2[i], Label.CENTER);
            lab2[i].setBackground(Color.gray);
            lab2[i].setFont(font);
            lab2[i].setLocation(k, 0);
            lab2[i].setSize(new Dimension(180, 30));
            BottomPanel.add(lab2[i]);
        }
 
        JPanel[] calendarPanel2 = new JPanel[5];
        for(int i = 0, k = 60; i < calendarPanel2.length; i++, k = k + 185){
            calendarPanel2[i] = new JPanel();
            cp2 = new CalendarPanel(calendarPanel2[i], 2015, mName2[i]);
            calendarPanel2[i] = cp2.getPanel();
            calendarPanel2[i].setLocation(k, 35);
            calendarPanel2[i].setSize(new Dimension(180, 250));
            BottomPanel.add(calendarPanel2[i]);
        }
 
        f.setLocation(50,50);
        f.setVisible(true);
    }
 
    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at md.iic.EditButton$ButtonsListener.actionPerformed(ColorButton.java:99)
    at java.awt.Button.processActionEvent(Unknown Source)
    at java.awt.Button.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(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)