import java.text.*;
import java.util.*;

public class DateUtils {

  public enum IntervalType {  Month, Week  }
  
  private DateUtils() {  }

  public static Calendar[] getDateIntervals(IntervalType type, Calendar reference) {
    if (reference == null) {
      reference = Calendar.getInstance();
    }
    Calendar startDate = (Calendar)reference.clone();
    Calendar endDate = (Calendar)reference.clone();

    if (type == IntervalType.Month) {
      // first date of the month
      startDate.set(Calendar.DATE, 1);
      // previous month
      startDate.add(Calendar.MONTH, -1);

      // first date of the month
      endDate.set(Calendar.DATE, 1);
      // previous month, last date
      endDate.add(Calendar.DATE, -1);
    }
    else {
      // previous week by convention (monday ... sunday)
      // you will have to adjust this a bit if you want
      // sunday to be considered as the first day of the week.
      //   start date : decrement until first sunday then 
      //   down to monday  
      int dayOfWeek = startDate.get(Calendar.DAY_OF_WEEK);
      while (dayOfWeek  != Calendar.SUNDAY) {
        startDate.add(Calendar.DATE, -1);
        dayOfWeek = startDate.get(Calendar.DAY_OF_WEEK);
      }
      while (dayOfWeek != Calendar.MONDAY) {
        startDate.add(Calendar.DATE, -1);
        dayOfWeek = startDate.get(Calendar.DAY_OF_WEEK);
      }

      // end date , decrement until the first sunday
      dayOfWeek = endDate.get(Calendar.DAY_OF_WEEK);
      while (dayOfWeek  != Calendar.SUNDAY) {
        endDate.add(Calendar.DATE, -1);
        dayOfWeek = endDate.get(Calendar.DAY_OF_WEEK);
      }
    }
    return new Calendar[] { startDate, endDate }; 
  }

  public static void main(String[] args) {
    try {
      SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

      System.out.println("** previous month (relative today)");
      Calendar [] results = DateUtils.getDateIntervals(IntervalType.Month, null);
      System.out.println(sdf.format(results[0].getTime()));
      System.out.println(sdf.format(results[1].getTime()));
      
      System.out.println("** previous week (relative today)");
      results = DateUtils.getDateIntervals(IntervalType.Week, null);
      System.out.println(sdf.format(results[0].getTime()));
      System.out.println(sdf.format(results[1].getTime()));

      System.out.println("** previous month (relative jan 1, 2007)");
      results = DateUtils.getDateIntervals(IntervalType.Month, 
        new GregorianCalendar(2007, 00, 1));
      System.out.println(sdf.format(results[0].getTime()));
      System.out.println(sdf.format(results[1].getTime()));
      
      System.out.println("** previous week (relative jan 1, 2007)");
      results = DateUtils.getDateIntervals(IntervalType.Week, 
        new GregorianCalendar(2007, 00, 1));
      System.out.println(sdf.format(results[0].getTime()));
      System.out.println(sdf.format(results[1].getTime()));

    }
    catch (Exception e) {
      e.printStackTrace();
    }
  }
  /*
    output :
    ** previous month (relative today)
    2008-06-01
    2008-06-30
    ** previous week (relative today)
    2008-06-30
    2008-07-06
    ** previous month (relative jan 1, 2007)
    2006-12-01
    2006-12-31
    ** previous week (relative jan 1, 2007)
    2006-12-25
    2006-12-31
  */  
}