Calendar,Date,Timestamp的使用及其转换

下面列出了Date，Timestamp ,String相互转换，以及通过Calendar创建时间的例子

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

public class CalenarAndTimeTest{
    public static void main(String[] args) throws ParseException{
        //创建Date对象
        Date date = new Date();
        //完整显示今天日期时间,  Date转化为String
        String str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS")).format(date);
        System.out.println(str);
        //String 转化为 Date
        date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS").parse(str);
        System.out.println(date);

        //创建Timestamp对象，Timestamp类是Date类的子类, Date 转化为 Timestamp
        Timestamp timestamp = new Timestamp(date.getTime());//需要使用long类型
        //Timestamp 转化为 Date
        Date date1 = timestamp;
        System.out.println(date1);
        //Timestamp 转 String
        str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS")).format(timestamp);
        //String转Timestamp
        timestamp =Timestamp.valueOf(str);

        //创建 Calendar对象
        Calendar calendar = Calendar.getInstance();
            //对calendar设置时间的方法
            //设置传入的时间格式
            SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd H:m:s");
            //指定一个日期
            Date date2= dateFormat.parse("2020-11-15 12:34:56");
            //对calendar设置为date所定的日期
            calendar.setTime(date);
            //按特定格式显示刚设置的时间
            str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS")).format(calendar.getTime());
            System.out.println(str);

        //另一种设置calendar的方式。
        //初始化Calendar对象
        calendar.set(2020,11,15,12,34,56);
        str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS").format(calendar.getTime()));
        System.out.println(str);

        //或者用Date来初始化 Calendar对象,new Date()会获得当前时间。
        calendar.setTime(new Date());
        str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS").format(calendar.getTime()));
        System.out.println(str);

        //创建一个Calendar用于比较时间
        Calendar calendarNew = Calendar.getInstance();

        //设定为5小时以前
        calendarNew.add(Calendar.HOUR,-5);
        System.out.println("时间比较：" + calendarNew.compareTo(calendar));//结果为calendarNew < calendar
    }
}

Calendar会可以进行时间运算

package com.zhou;

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

public class CalendarAndTimeTest1 {
    public static void main(String[] args) throws ParseException {
        //创建Calendar对象
        Calendar calendar = Calendar.getInstance();
        //设置传入的时间格式
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        //指定一个日期
        Date date = dateFormat.parse("2020-11-14 23:59:59");
        //为calendar设定为date所定的日期
        calendar.setTime(date);
        System.out.println(calendar.getTime());

        calendar.add(Calendar.SECOND,1);
        System.out.println(calendar.getTime());
    }
}

"C:\Program Files\Java\jdk1.8.0_131\bin\java.exe" "-javaagent:D:\IntelliJ IDEA 2018\lib\idea_rt.jar=56462:D:\IntelliJ IDEA 2018\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;C:\Users\zhoubiao\IdeaProjects\gui-study\out\production\gui-study" com.zhou.CalendarAndTimeTest1
Sat Nov 14 23:59:59 CST 2020
Sun Nov 15 00:00:00 CST 2020

进程完成，退出码 0

https://blog.csdn.net/joyous/article/details/9630893