SimpleDateFormat使用详解

SimpleDateFormat类继承关系

java.lang.Object
   |
   ----java.text.Format
   |
    +----java.text.DateFormat
   |
    +----java.text.SimpleDateFormat    

12小时制以及24小时制写法

import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Date;public class Test {public static void main(String[] args) {dateFormat();}public static void dateFormat() {String time1 = "2014-04-17 00:00";String time2 = "2014-04-17 15:00";Date date = new Date();SimpleDateFormat format12 = new SimpleDateFormat("yyyy-MM-dd hh:mm");SimpleDateFormat format24 = new SimpleDateFormat("yyyy-MM-dd HH:mm");    try {    //time1System.out.println("12小时制time1:"+format12.format(format12.parse(time1)));System.out.println("24小时制time1:"+format24.format(format24.parse(time1)));//time2System.out.println("12小时制time2:"+format12.format(format12.parse(time2)));System.out.println("24小时制time2:"+format24.format(format24.parse(time2)));//当前系统时间System.out.println("12小时制时间 :"+format12.format(date));System.out.println("24小时制时间 :"+format24.format(date));} catch (ParseException e) {e.printStackTrace();}}}

执行结果:

12小时制time1:2014-04-17 12:00
24小时制time1:2014-04-17 00:00
12小时制time2:2014-04-17 03:00
24小时制time2:2014-04-17 15:00
12小时制时间 :2014-04-17 07:34
24小时制时间 :2014-04-17 19:34

时间格式转换

public class Test {public static void main(String[] args) {Calendar calendar = Calendar.getInstance();  //静态方法getInstance()实例化日历对象long time = calendar.getTimeInMillis();System.out.println("当前系统时间:"+time);  //当前系统毫秒时间:1397736245451System.out.println("当前系统时间:"+getDate(time));  //当前系统时间:2014-04-17 20:04:05int year = calendar.get(Calendar.YEAR);System.out.println(year);  //2014int month = calendar.get(Calendar.MONTH);System.out.println(month+1);  //4int date = calendar.get(Calendar.DATE);System.out.println(date);  //17System.out.println(calendar.get(Calendar.DAY_OF_MONTH));  //17 这个月的第几天int hour12 = calendar.get(Calendar.HOUR);System.out.println(hour12);  //8int hour24 = calendar.get(Calendar.HOUR_OF_DAY);System.out.println(hour24);  //20}//时间格式转换public static String getDate(long str){Calendar calendar = Calendar.getInstance();calendar.setTimeInMillis(str);Date date = calendar.getTime();SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");return sdf.format(date);}}

public class Test {public static void main(String[] args) {SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");Calendar calendar = Calendar.getInstance();calendar.set(Calendar.YEAR, 2013);calendar.set(Calendar.MONTH, 3);calendar.set(Calendar.DAY_OF_MONTH, 15);Date date = calendar.getTime();System.out.println(sdf.format(date));  //2013-04-15}}

//Calendar转化为Date
Calendar calendar = Calendar.getInstance();
Date date = calendar.getTime();

//Date转化为Calendar
Date date = new Date();
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);