import java.time.DayOfWeek;
import java.time.LocalDate;

public class Main {

    public static void main(String[] args) {
        LocalDate date = LocalDate.now();
        int month = date.getMonthValue();
        int today = date.getDayOfMonth();
        System.out.println(month);

        date = date.minusDays(today - 1);
        System.out.println(date.getMonthValue());

        DayOfWeek weekday = date.getDayOfWeek();
        int value = weekday.getValue();
        System.out.println(value);

        System.out.println("Mon Tue Wed Thu Fri Sat Sun");
        for (int i = 1; i < value; i++) {
            System.out.print("    ");
        }
        while (date.getMonthValue() == month) {
            System.out.printf("%3d", date.getDayOfMonth());
            if (date.getDayOfMonth() == today) {
                System.out.printf("*");
            } else {
                System.out.print(" ");
            }
            date = date.plusDays(1);
            if (date.getDayOfWeek().getValue() == 1) {
                System.out.println();
            }
        }
    }
}

運行結果

5
5
2
Mon Tue Wed Thu Fri Sat Sun
      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