java使用Calendar类操作时间进行加减

Calendar是一个时间操作类，使用很方便

package com.example.hotelmanagement.controller;

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

/**
 * @Author: 宇
 * @introduction:
 * @catalogue: com.example.hotelmanagement.controller
 * @Date: 2021/6/2 11:19
 * @Version: 1.0
 */
public class Time {
    //操作时间，对时间进行相加减
    public static void main(String[] args) throws Exception {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        //当前时间
        Date date = new Date();
        System.out.println("===========================");
        System.out.println(sdf.format(date));
        //获取的是当前时间
        Calendar calendar = Calendar.getInstance();
        System.out.println("===========================");
        System.out.println(sdf.format(calendar.getTime()));
        //自定义一个时间
        String time = "10:10:10";
        SimpleDateFormat sdf1 = new SimpleDateFormat("HH:mm:ss");
        Calendar calendar1 = Calendar.getInstance();
        //对起进行赋值
        calendar1.setTime(sdf1.parse(time));
        System.out.println("===========================");
        System.out.println(sdf1.format(calendar1.getTime()));
        //获取指定时分秒
        int hour1 = calendar1.get(Calendar.HOUR);
        int minute1 = calendar1.get(Calendar.MINUTE);
        int second1 = calendar1.get(Calendar.SECOND);
        /**
         * 用自定义的calendar1给calendar赋值，
         * 默认为"+"
         * 前面带"-"为减去
         */
        //加上多长小时
        calendar.add(Calendar.HOUR, hour1);
        //减去多长分钟
        calendar.add(Calendar.MINUTE, -minute1);
        //加上多长秒
        calendar.add(Calendar.SECOND, +second1);
        System.out.println("===========================");
        System.out.println(sdf.format(calendar.getTime()));


    }
}

下面是输出结果