(Display a calendar) Write a program that displays the calendar for the current month. You can use the Prior and Next buttons to show the calendar of the previous or next month. Display the dates in the current month in black and display the dates in the previous month and next month in gray

MyCalendar.java

import java.awt.event.*;
import javax.swing.*;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.util.Calendar;
import java.util.GregorianCalendar;
import javax.swing.border.Border;
import javax.swing.border.LineBorder;

public class MyCalendar extends JFrame {
    
    Calendar cal1 = new GregorianCalendar();
    Calendar cal2 = new GregorianCalendar(
            cal1.get(Calendar.YEAR), cal1.get(Calendar.MONTH), 1);
    
    private CalendarPanel dc = new CalendarPanel(cal2);
    private JButton previous = new JButton("Previous");
    private JButton next = new JButton("Next");
    
    MyCalendar() {
        JPanel panel = new JPanel();
        panel.add(previous);
        panel.add(next);
        
        add(dc, BorderLayout.CENTER);
        add(panel, BorderLayout.SOUTH);
        
        next.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                remove(dc);
                dc = dc.moveToNextMonth();
                add(dc, BorderLayout.CENTER);
                repaint();
                revalidate();
            }
        });
        
        previous.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                remove(dc);
                dc = dc.moveToPreviousMonth();
                add(dc, BorderLayout.CENTER);
                repaint();
                revalidate();
            }
        });
    }
    
    public static void main(String[] args) {
        JFrame frame = new MyCalendar();
        frame.pack();
        frame.setResizable(false);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

class CalendarPanel extends JPanel {
    
    public Calendar calendar;
    private int currentYear;
    private int currentMonth;
    private int numOfDaysInMonth;
    private int starDay;
    private int previousMonth;
    
    public CalendarPanel(Calendar calendar) {
        this.calendar = calendar;
        
        setLayout(new BorderLayout());
        
        
        currentYear = calendar.get(Calendar.YEAR);
        currentMonth = calendar.get(Calendar.MONTH);
        numOfDaysInMonth = getMaximum(currentMonth);
        starDay = calendar.get(Calendar.DAY_OF_WEEK);
        previousMonth = getPreviousMonth(currentMonth);
        
        JLabel calendarHeader = new JLabel((currentMonth + 1) + "/" + currentYear);
        calendarHeader.setHorizontalAlignment(JLabel.CENTER);
        
        JPanel panel = new JPanel(new GridLayout(0, 7, 0, 0));
        Border border = new LineBorder(Color.BLACK, 1);
        
        JLabel l1 = new JLabel("Sunday");
        l1.setHorizontalAlignment(JLabel.CENTER);
        l1.setBorder(border);
        
        JLabel l2 = new JLabel("Monday");
        l2.setHorizontalAlignment(JLabel.CENTER);
        l2.setBorder(border);
        
        JLabel l3 = new JLabel("Tuesday");
        l3.setHorizontalAlignment(JLabel.CENTER);
        l3.setBorder(border);
        
        JLabel l4 = new JLabel("Wednesday");
        l4.setHorizontalAlignment(JLabel.CENTER);
        l4.setBorder(border);
        
        JLabel l5 = new JLabel("Thursday");
        l5.setHorizontalAlignment(JLabel.CENTER);
        l5.setBorder(border);
        
        JLabel l6 = new JLabel("Friday");
        l6.setHorizontalAlignment(JLabel.CENTER);
        l6.setBorder(border);
        
        JLabel l7 = new JLabel("Saturday");
        l7.setHorizontalAlignment(JLabel.CENTER);
        l7.setBorder(border);
        
        panel.add(l1);
        panel.add(l2);
        panel.add(l3);
        panel.add(l4);
        panel.add(l5);
        panel.add(l6);
        panel.add(l7);
        
        int i;
        
        int numOfDaysInPreviousMonth = getMaximum(previousMonth);
        int previousMonthDayToDisplay = numOfDaysInPreviousMonth - starDay + 2;
        
        for (i = 1; i < starDay; i++) {
            JLabel label = new JLabel(previousMonthDayToDisplay + "");
            label.setBorder(border);
            label.setHorizontalAlignment(JLabel.RIGHT);
            label.setForeground(Color.lightGray);
            panel.add(label);
            previousMonthDayToDisplay++;
        }
        
        for (int j = 1 ; j <= numOfDaysInMonth; j++, i++) {
            JLabel label = new JLabel(j + "");
            label.setBorder(border);
            label.setHorizontalAlignment(JLabel.RIGHT);
            panel.add(label);
        }
        
        for (int j = 1 ; i <= 42; j++, i++) {
            JLabel label = new JLabel(j + "");
            label.setBorder(border);
            label.setHorizontalAlignment(JLabel.RIGHT);
            label.setForeground(Color.LIGHT_GRAY);
            panel.add(label);
        }
        
        add(calendarHeader, BorderLayout.NORTH);
        add(panel, BorderLayout.CENTER);
    }
    
    private int getPreviousMonth(int month) {
        if (month == 0) {
            return 11;
        }
        
        return month - 1;
    }
    
    private int getMaximum(int month) {
        int maximum = 0;
        switch (month) {
            case 0: 
                maximum = 31;
                break;
            case 1: 
                if (isLeap())
                    maximum = 29;
                else
                    maximum = 28;
                break;
            case 2:
                maximum = 31;
                break;
            case 3:
                maximum = 30;
                break;
            case 4:
                maximum = 31;
                break;
            case 5:
                maximum = 30;
                break;
            case 6:
                maximum = 31;
                break;
            case 7:
                maximum = 31;
                break;
            case 8:
                maximum = 30;
                break;
            case 9:
                maximum = 31;
                break;
            case 10:
                maximum = 30;
                break;
            case 11:
                maximum = 31;
                break;
        }
        
        return maximum;
    }
    
    private boolean isLeap() {
        return (currentYear % 4 == 0 && currentYear % 100 != 0) || 
                currentYear % 400 == 0;
    }
    
    public CalendarPanel moveToPreviousMonth() {
        return new CalendarPanel(new GregorianCalendar(
                currentYear, 
                currentMonth - 1, 
                1));
    }
    
    public CalendarPanel moveToNextMonth() {
        return new CalendarPanel(new GregorianCalendar(
                currentYear, 
                currentMonth + 1, 
                1));
    }
    
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(500, 200);
    }
}