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Write a program to accept the year, month and the weekday name of the 1st day of that month and generate its calendar. 

import java.util.*;

class Calendar {
    String mnName, startDay;
    int y;
    int[] DAY_COUNT = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    String[] MONTH_NAME = {
            "January", "February", "March", "April", "May", "June", "July", "August", "September", "October",
            "November", "December"
    };
    String[] DAY_NAME = {
            "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
    };
    int[][] Cal = new int[5][7];

    Calendar(int year, String month, String day) {
        y = year;
        mnName = month.toLowerCase();
        startDay = day.toLowerCase();
    }

    private int indexOf(String[] S, String v) {
        for (int x = 0; x < S.length; x++)
            if (v.equalsIgnoreCase(S[x]))
                return x;
        return -1;
    }

    void makeCalendar() {
        int d = 0, start = 0;
        int mnIndex = indexOf(MONTH_NAME, mnName);
        if (y % 4 == 0 && mnIndex == 1)
            d = 29;
        else
            d = DAY_COUNT[mnIndex];
        start = indexOf(DAY_NAME, startDay);
        mnName = MONTH_NAME[mnIndex];
        for (int i = 0; i < d; i++) {
            int rw = (i + start) / 7, cl = (i + start) % 7;
            Cal[rw % 5][cl] = i + 1;
        }
    }

    void display() {
        System.out.println("\n\t----------------------------------------------------");
        System.out.println("\t\t\t " + mnName + " " + y);
        System.out.println("\t----------------------------------------------------");
        System.out.println("\tSUN\tMON\tTUE\tWED\tTHU\tFRI\tSAT");
        System.out.println("\t----------------------------------------------------");
        for (int i = 0; i < Cal.length; i++) {
            System.out.print("\t");
            for (int j = 0; j < Cal[0].length; j++) {
                int vl = Cal[i][j];
                System.out.printf("%s\t", vl != 0 ? vl : " ");
            }
            System.out.println();
        }
    }

    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter year : ");
        int y = sc.nextInt();
        System.out.print("Enter month name : ");
        String mName = sc.next();
        System.out.printf("Enter the week day name of 1st day of %s : ", mName);
        String wName = sc.next();
        Calendar a = new Calendar(y, mName, wName);
        a.makeCalendar();
        a.display();
        sc.close();
    }
}

Algorithm

void main()

  1. Initialize the scanner object to take user input
  2. Enter the current year into a integer y
  3. Enter the month current month name in a variable mName of String typ
  4. Enter the starting day of the week and store it in wName of String type
  5. make a object of class Calendar and pass values y, nName, wName as Constructor parameters.
  6. Call the methods makeCalendar() and display().

int indexOf(String[] S, String v)

  1. Start for loop with x=0 and condition x<S.length and x=x+1
  2. if the value at current index(x) is equal to v then return x
  3. End for loop.
  4. return -1, as no matching element is found.

void makeCalendar()

  1. Initialize d=0 and start=0
  2. Calculate mnIndex as indexOf(MONTH_NAME, mnName)
  3. If it is leap year and month is february then d=19 else it d=DAY_COUNT[mnIndex].
  4. Calculate start as indexOf(DAY_NAME, startDay)
  5. Calculate mnName as MONTH_NAME[mnIndex]
  6. Start for loop with i=0 and condition as i<d and i=i+1
  7. Calculate rw = (i+start)/7 (This is the row of the matrix for current day)
  8. Calculate c; = (i+start)%7 (This is the column of the matrix for current day)
  9. Store Cal[rw % 5][cl] = i + 1
  10. End for loop.

void display()

  1. Print the relevant markup, i.e. month name, yaer, days of week.
  2. Intertate over the Double Dimensional Array Cal and print it.(This is the actual Calendar printed)

Variable Description

Name Type Uses
global
mnName String to store the entered month name
startDay String name of staring weekday
y int to store entered year
DAY_COUNT int[] this stores the number of days in month
MONTH_NAME Names of the 12 months
DAY_NAME Names of weekdays
Cal int[][] This a 5 by 7 Matrix to store thr calendar
int indexOf()
S String[] This is the string array which is to be searched
v String Value to search for in the array
x int this is the index of array where element may be found
void makeCalendar()
d int to store the number of days of the current month
start int to store the starting day of the week
mnIndex int this stores the month index
mnName int this stores the month name
void display()
i, j int counter variables to iterate over the calendar matrix
void main()
sc Scanner object to take user input
y int to store entered year
mName String to store entered month name
wName String to store starting day of the week
a Calendar object to call methods