Java Data Type - 如何使用本地化时，以全四位数显示年份

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Locale;

public class Main {
  private static String setDate(int day, Locale locale) {
    Calendar cal = Calendar.getInstance();
    cal.add(Calendar.DATE, +day);
    DateFormat df = DateFormat.getDateInstance(DateFormat.SHORT, locale);
    if (df instanceof SimpleDateFormat) {
      SimpleDateFormat sdf = (SimpleDateFormat) df;
      // To show Locale specific short date expression with full year
      String pattern = sdf.toPattern().replaceAll("y+", "yyyy");
      sdf.applyPattern(pattern);
      return sdf.format(cal.getTime());
    }
    String formattedDate = df.format(cal.getTime());
    return formattedDate;
  }

  public static void main(String[] args) {
     System.out.println(setDate(1, Locale.JAPAN));
  }
}