Java日期计算

package com.zl;

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

//计算输入的日期与当前时间相差多少年，月，日
public class Demo {
	
	public static void main(String[] a){
		getYearNumber(2000, 9, 1);
	}
	
	private static Calendar calendar = Calendar.getInstance();
	
	public static void getYearNumber(int year,int month,int day){
		//得到当前年
		int nowyear = calendar.get(Calendar.YEAR);
		//得到当年月--ps:月从0开始，所以+1
		int nowmonth = calendar.get(Calendar.MONTH)+1;
		//得到当前日
		int nowday = calendar.get(Calendar.DAY_OF_MONTH);
		//得到输入日期与当前日期年差
		int resultyear = nowyear - year;
		//如果输入日期大于当前日期   则退出
		if(resultyear<0){
			System.out.println("对不起！您输入的年份大于现在的当前年份！");
			System.exit(-1);
		}
		//开始计算相差的天数
		//封装当前日期
		calendar = new GregorianCalendar(nowyear,nowmonth,nowday);
		//得到当前日期的Date类型
		Date firstDate = calendar.getTime();
		//封装输入日期
		GregorianCalendar calendarone = new GregorianCalendar(year,month,day);
		//得到输入日期的Date类型
		Date secondDate = calendarone.getTime();
		//得到两个日期的时间差
		long longresultday = firstDate.getTime() - secondDate.getTime();
		//计算出日差
		int resultday=(int)(longresultday/86400/1000);
		//计算相差的月份
		int resultmonth = 0;
		while(calendar.get(calendar.YEAR)!=calendarone.get(calendarone.YEAR)||
		   calendar.get(calendar.MONTH)!=calendarone.get(calendarone.MONTH)
		   ){
			calendarone.add(calendarone.MONTH, 1);
			resultmonth++;
		}
		System.out.println("您输入的日期和现在相差："+resultyear+"年");
		System.out.println("您输入的日期和现在相差："+resultmonth+"月");
		System.out.println("您输入的日期和现在相差："+resultday+"天");
	}
}