public static Calendar getInstance()
{
    Calendar cal = createCalendar(TimeZone.getDefaultRef(), Locale.getDefault(Locale.Category.FORMAT));
    cal.sharedZone = true;
    return cal;
}
private static Calendar createCalendar(TimeZone zone, Locale aLocale)
{
   Calendar cal = null;
   String caltype = aLocale.getUnicodeLocaleType("ca");
    if (caltype == null) {
        // Calendar type is not specified.
        // If the specified locale is a Thai locale,
        // returns a BuddhistCalendar instance.
        if ("th".equals(aLocale.getLanguage())
                && ("TH".equals(aLocale.getCountry()))) {
            cal = new BuddhistCalendar(zone, aLocale);
        } else {
            cal = new GregorianCalendar(zone, aLocale);
        }
    } else if (caltype.equals("japanese")) {
        cal = new JapaneseImperialCalendar(zone, aLocale);
    } else if (caltype.equals("buddhist")) {
        cal = new BuddhistCalendar(zone, aLocale);
    } else {
        // Unsupported calendar type.
        // Use Gregorian calendar as a fallback.
        cal = new GregorianCalendar(zone, aLocale);
    }
 return cal;
}

/* private생성자와 정적 변수를 이용하여 싱글톤을 만드는 방법*/
public class Singleton{
  private static Singleton uniqueInstance;
  private Singleton(){}
  public static Singleton getInstance(){
    if(uniqueInstance == null) uniqueInstance = new Singleton();
    return uniqueInstance;
  }
}

public class Singleton{
  private static Singleton uniqueInstance;
  private Singleton(){}
  public static synchronized Singleton getInstance(){
    if(uniqueInstance == null) uniqueInstance = new Singleton();
    return uniqueInstance;
  }
}

public class Singleton{
  private static Singleton uniqueInstance = new Singleton();
  private Singleton(){}
  public static Singleton getInstance(){
    return uniqueInstance;
  }
}

public class Singleton{
  private volatile static Singleton uniqueInstance;
  private Singleton(){}
  public static Singleton getInstance(){
    if(uniqueInstance == null) {
      synchronized(Singleton.class){
        if(uniqueInstance == null) {
          uniqueInstance = new Singleton();
        }
      }
    }
    return uniqueInstance;
  }
}