(Display calendars) Rewrite the PrintCalendar class in Listing 6.12 to display a calendar for a specified month using the Calendar and GregorianCalendar classes. Your program receives the month and year from the command line. For example:

/*********************************************************************************
* (Display calendars) Rewrite the PrintCalendar class in Listing 6.12 to display *
* a calendar for a specified month using the Calendar and GregorianCalendar      *
* classes. Your program receives the month and year from the command line. For   *
* example:                                                                       *
*                                                                                *
* java Exercise13_04 5 2016                                                      *
*                                                                                *
* This displays the calendar shown in Figure 13.9.                               *
*                                                                                *
* You also can run the program without the year. In this case, the year is the   *
* current year. If you run the program without specifying a month and a year,    *
* the month is the current month.                                                *
*********************************************************************************/
import java.util.*;

public class Exercise_13_04 {
	/** Main method */
	public static void main(String[] args) {
		// Check java command line usage 
		if (args.length != 2) {
			System.out.println("Usage: java Exercise_13_04 month year");
			System.exit(1);
		}


		// Crate a Caleander object
		Calendar calendar = new GregorianCalendar(Integer.valueOf(args[1]), 
			Integer.valueOf(args[0]) - 1, 1);

		// Display calander header
		printHeader(calendar); 
		

		// Pad space before the first day of the month
		for (int i = 1; i < calendar.get(Calendar.DAY_OF_WEEK); i++) 
			System.out.print("    ");

		// Print days in month
		while (calendar.get(Calendar.DATE) <
			calendar.getActualMaximum(Calendar.DATE)) {

			if (calendar.get(Calendar.DAY_OF_WEEK) == 7)
				System.out.printf("%4d\n", calendar.get(Calendar.DATE));
			else
				System.out.printf("%4d", calendar.get(Calendar.DATE));

			// Add a day
			calendar.add(Calendar.DATE, 1);
		}
		System.out.printf("%4d\n", calendar.get(Calendar.DATE));
	}

	/** Returns an String array of month names */
	public static String[] getMonths() {
		String[] months = {"January", "February", "March", "April", "May", "June", 
			"July", "August", "September", "October", "November", "December"};
		return months;
	}

	/** Display calander header */
	public static void printHeader(Calendar calendar) {
		// Create an array of month names
		String[] months = getMonths();

		// Center month and year center format
		int length = 29 / 2 - (months[calendar.get(Calendar.MONTH)].length() / 2 + 3);
		System.out.println();
		for (int i = 0; i < length; i++)
			System.out.print(" ");
		System.out.println(months[calendar.get(Calendar.MONTH)] + ", " + 
			calendar.get(Calendar.YEAR));

		// Print week day names
		System.out.println("-----------------------------");
		System.out.println(" Sun Mon Tue Wed Thu Fri Sat");
	}

}