西暦を和暦に変換する（1月1日の年号を取得）

changeYear.java

import java.time.chrono.JapaneseDate;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class changeYear {
        public static void main(String[] args) {
            System.out.println(changeYearToEra(2014));
            System.out.println(changeYearToEra(1989));
            System.out.println(changeYearToEra(1990));
        }

        public static String changeYearToEra(int year) {
            JapaneseDate japaneseDate = JapaneseDate.of(year, 1, 1);
            DateTimeFormatter formatter = DateTimeFormatter.ofPattern("Gy年", Locale.JAPANESE);
            return formatter.format(japaneseDate);
        }
}