Java Calendar isSet方法

package com.codingdict;

import java.util.*;

public class CalendarDemo {
   public static void main(String[] args) {

      // create a calendar
      Calendar cal = Calendar.getInstance();

      // display the current calendar
      System.out.println("Current Day is " + cal.get(Calendar.DAY_OF_MONTH));

      // determine if the given calendar field has a value set
      boolean b = cal.isSet(Calendar.DAY_OF_MONTH);
      System.out.println("Day of month is set: " + b);

      // clear day of month
      cal.clear(Calendar.DAY_OF_MONTH);

      // determine if the given calendar field has a value set
      b = cal.isSet(Calendar.DAY_OF_MONTH);
      System.out.println("Day of month is set: " + b);
   }
}