对系统时间的操作

package com.ob;

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

public class DateTest {

public static void main(String[] args) throws ParseException {
Calendar now = Calendar.getInstance();
System.out.println("年: " + now.get(Calendar.YEAR));
System.out.println("月: " + (now.get(Calendar.MONTH) + 1) + "");
System.out.println("日: " + now.get(Calendar.DAY_OF_MONTH));
System.out.println("时: " + now.get(Calendar.HOUR_OF_DAY));
System.out.println("分: " + now.get(Calendar.MINUTE));
System.out.println("秒: " + now.get(Calendar.SECOND));
System.out.println("当前时间毫秒数：" + now.getTimeInMillis());
System.out.println(now.getTime());

Date d = new Date();
System.out.println(d);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateNowStr = sdf.format(d);
System.out.println("格式化后的日期：" + dateNowStr);

String str = "2012-1-13 17:26:33";  //要跟上面sdf定义的格式一样
Date today = sdf.parse(str);
System.out.println("字符串转成日期：" + today);
}
}

输出结果：

年: 2017

月: 19

日: 13

时: 17

分: 28

秒: 19

当前时间毫秒数：1326446899902

Fri October 13 17:28:19 CST 2017

Fri October13 17:28:19 CST 2017

格式化后的日期：2017-10-13 17:28:19

字符串转成日期：Fri October 13 17:26:33 CST 2017