import java.awt.*;
import java.awt.event.*;
import java.text.*;
import java.util.*;
import javax.swing.*;

public class MyWidget extends JFrame implements ActionListener, Runnable {
    String[] w = { "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun", };
    String[] m = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec", };
    JPanel p2;
    JLabel lblMonthYear, lblTime;
    JButton btnPrevMonth, btnNextMonth;
    int year, month;
    Calendar calendar;
    DateFormat formatter;

    public MyWidget() {
        this.setResizable(false);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLayout(new BorderLayout());
        JPanel p1 = new JPanel(new BorderLayout());
        this.p2 = new JPanel(new GridLayout(0, 7));
        this.calendar = Calendar.getInstance();
        this.year = calendar.get(Calendar.YEAR);
        this.month = calendar.get(Calendar.MONTH);
        this.btnPrevMonth = new JButton("<");
        this.btnPrevMonth.addActionListener(this);
        this.lblMonthYear = new JLabel();
        this.lblMonthYear.setHorizontalAlignment(JLabel.CENTER);
        this.btnNextMonth = new JButton(">");
        this.btnNextMonth.addActionListener(this);
        p1.add(btnPrevMonth, BorderLayout.WEST);
        p1.add(lblMonthYear, BorderLayout.CENTER);
        p1.add(btnNextMonth, BorderLayout.EAST);
        this.lblTime = new JLabel();
        this.formatter = new SimpleDateFormat("HH:mm:ss");
        JPanel pnlHeader = new JPanel(new BorderLayout());
        JPanel pnlCenter = new JPanel(new BorderLayout());
        JPanel pnlFooter = new JPanel();
        pnlHeader.add(p1, BorderLayout.NORTH);
        pnlCenter.add(p2, BorderLayout.CENTER);
        pnlFooter.add(lblTime);
        this.add(pnlHeader, BorderLayout.NORTH);
        this.add(pnlCenter, BorderLayout.CENTER);
        this.add(pnlFooter, BorderLayout.SOUTH);
        showCalendar();
        this.pack();
    }

    private void showCalendar() {
        p2.removeAll();
        p2.repaint();
        for(int i=0; i<7; i++) {
            JLabel l = new JLabel(w[i]);
            l.setHorizontalAlignment(JLabel.CENTER);
            p2.add(l);
        }
        this.lblMonthYear.setText(m[month] + " " + year);

        JLabel[][] days = new JLabel[7][7];
        calendar.set(Calendar.YEAR, year);
        calendar.set(Calendar.MONTH, month);
        calendar.set(Calendar.DATE, 1);

        int dayOfWeekOn1st = (calendar.get(Calendar.DAY_OF_WEEK) + 5) % 7;
        for(int i=0; i<dayOfWeekOn1st; i++) {
            days[0][i] = new JLabel();
            days[0][i].setHorizontalAlignment(JLabel.CENTER);
            p2.add(days[0][i]);
        }
        int day = 1;
        for(int i=dayOfWeekOn1st; i<7; i++) {
            days[0][i] = new JLabel("" + (day++));
            days[0][i].setHorizontalAlignment(JLabel.CENTER);
            p2.add(days[0][i]);
        }
here: for(int r=1; r<7; r++) {
            days[r] = new JLabel[7];
            for(int i=0; i<7; i++) {
                if(day > calendar.getActualMaximum(Calendar.DATE)) { break here; }
                days[r][i] = new JLabel("" + day);
                days[r][i].setHorizontalAlignment(JLabel.CENTER);
                day += 1;
                p2.add(days[r][i]);
            }
        }
    }

    @Override public void run() {
        for( ; ; ) {
            try {
                Calendar now = Calendar.getInstance();
                lblTime.setText(formatter.format(now.getTime()));
                Thread.sleep(500);
            } catch(InterruptedException ex) {
                ex.printStackTrace();
            }
        }
    }

    @Override public void actionPerformed(ActionEvent e) {
        Object source = e.getSource();
        if(source == btnNextMonth) {
            if(month == 11) {
                year += 1;
                month = 0;
            } else {
                month += 1;
            }
            showCalendar();
        } else if(source == btnPrevMonth) {
            if(month == 0) {
                year -= 1;
                month = 11;
            } else {
                month -= 1;
            }
            showCalendar();
        }
    }

    public static void main(String[] args) {
        MyWidget self = new MyWidget();
        new Thread(self).start();
        self.setVisible(true);
    }
}