Java日期时间操作的方法

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()));
  }
}