Java学习笔记-Calendar和Date使用

1.获取当前时间

Calendar cal = Calendar.getInstance();
System.out.println(cal.getTime());

Date date=new Date();
System.out.println(date);

输出结果一致：

Tue Jan 05 11:18:46 CST 2021
Tue Jan 05 11:18:46 CST 2021

2.获取年月日

date.getDay()等其他get年月日的方法已经废弃，当然啦，如果非要用，也不是不可以。

但目前都推荐用Calendar去获取年月日

//年
System.out.println(calendar.get(Calendar.YEAR));
//月
System.out.println(calendar.get(Calendar.MONTH));
//日
System.out.println(calendar.get(Calendar.DAY_OF_MONTH));
//时
System.out.println(calendar.get(Calendar.HOUR_OF_DAY));
//分
System.out.println(calendar.get(Calendar.MINUTE));
//秒
System.out.println(calendar.get(Calendar.SECOND));

3.日期格式化

Date date = new Date();
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
System.out.println(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(date));

输出如下：

2021-01-05 11:32:44
 

Date date = new Date();
System.out.println(date);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
// Date类型转换成 yyyy-MM-dd HH:mm:ss类型
System.out.println(sdf.format(date));

输出如下：

Tue Jan 05 11:33:33 CST 2021
2021-01-05 11:33:33
 

4.日期新增xx年/月/日/小时/秒

Date date=new Date();
System.out.println(date);
System.out.println(DateUtils.addDays(date, -7));
System.out.println(DateUtils.addMonths(date, -1));
System.out.println(DateUtils.addHours(date, -1));
System.out.println(DateUtils.addMinutes(date, -1));
System.out.println(DateUtils.addYears(date, -1));

输出如下：

Tue Jan 05 11:36:32 CST 2021
Tue Dec 29 11:36:32 CST 2020
Sat Dec 05 11:36:32 CST 2020
Tue Jan 05 10:36:32 CST 2021
Tue Jan 05 11:35:32 CST 2021
Sun Jan 05 11:36:32 CST 2020

Date date = new Date();
System.out.println((new SimpleDateFormat("yyyy-MM-dd")).format(date));
Calendar cal = Calendar.getInstance();
cal.setTime(date);
//年
cal.add(Calendar.YEAR, 3);
System.out.println((new SimpleDateFormat("yyyy-MM-dd")).format(cal.getTime()));
//天
cal.add(Calendar.DATE, 3);
System.out.println((new SimpleDateFormat("yyyy-MM-dd")).format(cal.getTime()));

输出如下：

2021-01-05
2024-01-05
2024-01-08