Java日期时间操作的一些方法

1. 获得Calendar实例:

Calendar c = Calendar.getInstance();

2. 定义日期/时间的格式:

SimpleDateFormat sdf =new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

3. 把日期/时间转换成固定格式,使用SimpleDateFormat的format()方法:

String datetime = sdf.format(c.getTime());

4. 把字符串转换成日期/时间,使用SimpleDateFormat的parse()方法:

Date d = sdf3.parse("2016-08-08 16:43:00");

5. 日期/时间的增加,减少,使用Calendar的add()方法,如将日期减少100天:

c.add(Calendar.DATE, -100);

6. 日期/时间的设置,使用Calendar的set()方法,如将小时设置为0时:

c.set(Calendar.HOUR_OF_DAY, 0);

例子:

package myCalendar;

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

public class myCalendar {
    public static void main(String args[]) throws Exception{
        Calendar c = Calendar.getInstance();
        
        SimpleDateFormat sdf1 =new SimpleDateFormat("yyyyMMdd");
        SimpleDateFormat sdf2 =new SimpleDateFormat("HHmmss");
        SimpleDateFormat sdf3 =new SimpleDateFormat("yyyyMMddHHmmss");
        SimpleDateFormat sdf4 =new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        
        String date = sdf1.format(c.getTime());
        System.out.println(date);
        String time = sdf2.format(c.getTime());
        System.out.println(time);
        
        String dt = "20160808162405";
        Date d = sdf3.parse(dt);
        dt = sdf4.format(d);
        
        c.setTime(d);
        c.add(Calendar.DATE, -100);
        c.set(Calendar.HOUR_OF_DAY, 0);
        c.set(Calendar.MINUTE, 0);
        c.set(Calendar.SECOND, 0);
        System.out.println("100天前:" + sdf4.format(c.getTime()));
        c.add(Calendar.DATE, 200);
        c.set(Calendar.HOUR_OF_DAY, 0);
        c.set(Calendar.MINUTE, 0);
        c.set(Calendar.SECOND, 0);
        System.out.println("100天后:" + sdf4.format(c.getTime()));
    }
}

运行结果如下: