java中对日期进行加减操作

package cn.cfm.demo.Test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

/**
 * @Description: 对日期进行加减操作
 * @Author: 
 * @Date: 2021/2/20
 */
public class DataShield {

    public static void main(String[] args) throws ParseException {

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        //获取系统日期
        Calendar rightNow = Calendar.getInstance();
        //指定某一天，比如2021-02-16
        Date shouldDate = sdf.parse("2021-02-16");
        //系统日期减少或者增加几天
        rightNow.add(Calendar.DATE, -9);
        System.out.println(sdf.format(rightNow.getTime()));

        Calendar rightNow2 = Calendar.getInstance();
        rightNow2.add(Calendar.DATE, -4);
        System.out.println(sdf.format(rightNow2.getTime()));

        System.out.println("=========================");
        System.out.println(sdf.parse(sdf.format(rightNow.getTime())).getTime());
        System.out.println(shouldDate.getTime());
        System.out.println(rightNow2.getTime().getTime());
        //sdf.parse(sdf.format(rightNow.getTime())).getTime()指以系统日期减少几天后，获取它的日期的getTime()而不是当前时间的getTime()
        if(sdf.parse(sdf.format(rightNow.getTime())).getTime() <= shouldDate.getTime()
                && shouldDate.getTime() <= rightNow2.getTime().getTime()) {
            System.out.println("成功");
        }else{
            System.out.println("失败");
        }

    }

}

输出结果

注意红框中的值，这样得到的是获取它的日期的getTime()而不是当前时间的getTime()