clone() method in java.util.Calendar not working properly

Name: mc57594 Date: 01/28/97


When modifying a cloned object instance that extends
  Calendar (e.g. GregorianCalendar), those modifications will also
  be reflected in the original object instance. Could this be an
  example of shallow cloning? Example to follow:

import java.util.GregorianCalendar ;

public class CalendarBug {

   public static void main(String[] args)
   {
      GregorianCalendar cal1 = new GregorianCalendar() ;
      GregorianCalendar cal2 = (GregorianCalendar) cal1.clone() ;

      printdate(cal1, "cal1: ") ;
      printdate(cal2, "cal2 - cloned(): ") ;
      cal2.add(GregorianCalendar.DATE, 1) ;
      printdate(cal1, "cal1 after adding 1 day:") ;
      printdate(cal2, "cal2 should be unmodified:") ;
   }

   private static void printdate(GregorianCalendar cal, String string)
   {
      System.out.print(string);
      System.out.print("" + cal.get(GregorianCalendar.MONTH)) ;
      int date = cal.get(GregorianCalendar.DATE) + 1 ;
      System.out.print("/" + date) ;
      System.out.println("/" + cal.get(GregorianCalendar.YEAR)) ;
   }
}
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