Swap Value of an Array in a Loop

Question

I was trying to build a beginner calendar exercise project and all I want is if last date of January ends on Sunday then start next month from Monday. Here is my code;

 public static void main(String[] args) 
    {

        String[] months= {"January","Febuary","March","April","May","June"
                   ,"July","August","september","October","November"
                   ,"December"
                 }; 
        String[] weekdays= {"Sun","Mon","Tue","Wed","Thu","Fri","Sat"};

        int x;

        for(int k=0;k<12;k++) 
          { 
            if(months[k]=="April" ||months[k]=="june" ||months[k]=="September" ||months[k]=="November")
                {x=30;}
            else if(months[k]=="Febuary") 
                {x=28;}
            else {x=31;}

            System.out.print(months[k]+"\n");


           for(int i=0;i<weekdays.length;i++) 
             {    
              System.out.print("\t"+weekdays[i]);
             }System.out.println();

           for(int m=1;m<=x;m++) {

               if(((m-1) %7) == 0)  //line break after 7 characters
               {
                   System.out.println();
               }
               System.out.print("\t"+m);
           }
           System.out.println();
    }
  }

Answer 1

I think you use not correct approach. Working with dated relates to working with Locale, because all these names like name for the month, weekdays in different format are already in the JVM. You should use it:

public static void printCalendar(LocalDate date, Locale locale) {
    DateFormatSymbols symbols = new DateFormatSymbols(locale);
    WeekFields weekFields = WeekFields.of(locale);

    printMonthName(symbols, date);
    printWeekdayNames(symbols, weekFields);
    printWeekdays(weekFields, date);
}

private static void printMonthName(DateFormatSymbols symbols, LocalDate date) {
    System.out.println(symbols.getMonths()[date.getMonthValue() - 1]);
}

private static void printWeekdayNames(DateFormatSymbols symbols, WeekFields weekFields) {
    String[] weekdays = symbols.getShortWeekdays();
    DayOfWeek firstDayOfWeek = weekFields.getFirstDayOfWeek();
    int offs = firstDayOfWeek == DayOfWeek.SUNDAY ? 1 : firstDayOfWeek.ordinal() + 2;

    for (int i = 0; i < 7; i++)
        System.out.print('\t' + (offs + i >= weekdays.length ? weekdays[(offs + i) % 7] : weekdays[offs + i]));

    System.out.println();
}

private static void printWeekdays(WeekFields weekFields, LocalDate date) {
    LocalDate cur = date.withDayOfMonth(1).with(weekFields.dayOfWeek(), 1);
    boolean stop = false;

    do {
        if (cur.getMonthValue() == date.getMonthValue())
            System.out.format("\t%2d", cur.getDayOfMonth());
        else
            System.out.format("\t  ");

        cur = cur.plusDays(1);

        if (cur.getDayOfWeek() == weekFields.getFirstDayOfWeek()) {
            System.out.println();
            stop = cur.getMonthValue() != date.getMonthValue();
        }
    } while (!stop);
}

Test1:

printCalendar(LocalDate.of(2018, Month.DECEMBER, 17), Locale.US);

December
    Sun Mon Tue Wed Thu Fri Sat
                             1
     2   3   4   5   6   7   8
     9  10  11  12  13  14  15
    16  17  18  19  20  21  22
    23  24  25  26  27  28  29
    30  31

Test2:

printCalendar(LocalDate.of(2018, Month.DECEMBER, 17), Locale.ITALIAN);

dicembre
    lun mar mer gio ven sab dom
                         1   2
     3   4   5   6   7   8   9
    10  11  12  13  14  15  16
    17  18  19  20  21  22  23
    24  25  26  27  28  29  30
    31

Answer 2

Your program still needs some adjustments: 1. The first day of the year can be sunday or other day of the week. 2. If the last day of the of the month is sunday, you should continue the order and not starting with sunday from the beginning.

I will propose you to adjust you current code, or you can use an existing library https://www.javatpoint.com/java-util-calendar.