Pegar a Segunda-feira da data passada!

import java.util.*;

public class Segunda {

      public static void main(String[] args) {

            Calendar cal = previousMonday(new GregorianCalendar());

            System.out.println(cal);

      }

      public static Calendar previousMonday(Calendar calendar) {

            Calendar c = (Calendar)calendar.clone();

            while (c.get(Calendar.DAY_OF_WEEK) != Calendar.MONDAY)
                  c.add(Calendar.DATE, -1);

            return c;
      }


}