Here you can find the source of getYearCount(String from, String to)
public static int getYearCount(String from, String to) throws Exception
//package com.java2s; //License from project: Open Source License import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.Locale; public class Main { private static final SimpleDateFormat FORMAT = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd"); public static int getYearCount(String from, String to) throws Exception { return getYearCount(from, to, DATE_FORMAT.toPattern()); }//from ww w .ja v a2 s . co m public static int getYearCount(String from, String to, String format) throws Exception { Date fromDate = dateFormatCheck(from, format); Date toDate = dateFormatCheck(to, format); // if two date are same, return 0. if (fromDate.compareTo(toDate) == 0) return 0; SimpleDateFormat yearFormat = new java.text.SimpleDateFormat("yyyy", java.util.Locale.KOREA); int fromYear = Integer.parseInt(yearFormat.format(fromDate)); int toYear = Integer.parseInt(yearFormat.format(toDate)); int result = 0; result += (toYear - fromYear); return result; } public static Date dateFormatCheck(String source, String format) throws ParseException { if (source == null) { throw new ParseException("date string to check is null", 0); } if (format == null) { throw new ParseException("format string to check date is null", 0); } SimpleDateFormat formatter = new SimpleDateFormat(format, Locale.KOREA); Date date = null; try { date = formatter.parse(source); } catch (ParseException e) { throw new ParseException(" wrong date:\"" + source + "\" with format \"" + format + "\"", 0); } if (!formatter.format(date).equals(source)) { throw new ParseException("Out of bound date:\"" + source + "\" with format \"" + format + "\"", 0); } return date; } public static String format(Date date) { return FORMAT.format(date); } public static Date parse(String datetime) { try { return FORMAT.parse(datetime); } catch (ParseException e) { return new Date(); } } }