Java时间差计算小程序

package com.example.demo.controller;

import com.example.demo.Demoboot0826Application;
import org.springframework.boot.SpringApplication;

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

public class TestJia {

    public static void main(String[] args) throws ParseException {
        System.out.println("today is : " + new java.util.Date());
//        calculateTimeDifferenceBySimpleDateFormat();

        System.out.println("UUID is : " + UUID.randomUUID());

        {
            Calendar now = Calendar.getInstance();
            System.out.println("today is : " + new java.util.Date());
            System.out.println("280 days : now is :   " + now.getTime());
            int day = 280;
//            day = 310;
            now.set(Calendar.DATE, now.get(Calendar.DATE) + day);
            Date after = now.getTime();
            System.out.println("after is : " + after);
        }
        {

            Calendar now = Calendar.getInstance();
            System.out.println("310 days:  now is :   "   + now.getTime());
            int day = 310;
            now.set(Calendar.DATE, now.get(Calendar.DATE) + day);
            Date after = now.getTime();
            System.out.println("after is : " + after);
        }
        {

            Calendar now = Calendar.getInstance();
            System.out.println("37 week:  now is :   "   + now.getTime());
            int day = 37*7;
            now.set(Calendar.DATE, now.get(Calendar.DATE) + day);
            Date after = now.getTime();
            System.out.println("after is : " + after);
        }
        {

            Calendar now = Calendar.getInstance();
            System.out.println(" 42 week : now is :   "   + now.getTime());
            int day = 42*7;
            now.set(Calendar.DATE, now.get(Calendar.DATE) + day);
            Date after = now.getTime();
            System.out.println("after is : " + after);
        }
    }

    
    public static void calculateTimeDifferenceBySimpleDateFormat() throws ParseException {
        SimpleDateFormat simpleFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm");
        
        Date fromDate1 = new Date();//simpleFormat.parse("2018-03-01 12:00");
        Date toDate1 = simpleFormat.parse("2018-03-12 12:00");
        long from1 = fromDate1.getTime();
        long to1 = toDate1.getTime();
        int days = (int) ((to1 - from1) / (1000 * 60 * 60 * 24));
        System.out.println("两个时间之间的天数差为：" + days);

        
        Date fromDate2 = simpleFormat.parse("2018-03-01 12:00");
        Date toDate2 = simpleFormat.parse("2018-03-12 12:00");
        long from2 = fromDate2.getTime();
        long to2 = toDate2.getTime();
        int hours = (int) ((to2 - from2) / (1000 * 60 * 60));
        System.out.println("两个时间之间的小时差为：" + hours);

        
        Date fromDate3 = simpleFormat.parse("2018-03-01 12:00");
        Date toDate3 = simpleFormat.parse("2018-03-12 12:00");
        long from3 = fromDate3.getTime();
        long to3 = toDate3.getTime();
        int minutes = (int) ((to3 - from3) / (1000 * 60));
        System.out.println("两个时间之间的分钟差为：" + minutes);
    }
}