java笔记------日期API

涉及的一些api:

Calendar calendar = Calendar.getInstance();

calendar.getTime();
calendar.setTime(date);
calendar.set(Calendar.YEAR,2000);
calendar.get(Calendar.DATE);
calendar.add(Calendar.DAY_OF_YEAR, 10);
calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
calendar1.after(calendar2);
calendar.getTimeInMillis();

SimpleDateFormat sdf = new SimpleDateFormat();

sdf.parse();
sdf.format();

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

String strTime = sdf.format(date);

date = sdf.parse(strTime);

举例及说明如下代码：

 1 package test;
 2
 3 import java.text.ParseException;
 4 import java.text.SimpleDateFormat;
 5 import java.util.Calendar;
 6 import java.util.Date;
 7
 8 public class DateDemo {
 9
10     public static void main(String[] args) throws ParseException {
11         Date date = new Date();
12
13         //当前时间毫秒值，long类型
14         long numTime = date.getTime();
15         System.out.println(numTime);
16
17         //以"yyyy-MM-dd  HH:mm:ss E" 格式 构造SimpleDateFormat的对象
18         SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd  HH:mm:ss E");
19
20         // 根据Date类型对象  生成sdf中的格式（构造方法中指定了）的字符串时间
21         String strTime = sdf.format(date);
22         System.out.println(strTime);
23
24         //从字符串strTime 以sdf中的格式（构造方法中指定了） 生成 Date类型对象
25         date = sdf.parse(strTime);
26         System.out.println(date);
27
28         //Calendar是抽象类，不能直接new生成
29         Calendar calendar = Calendar.getInstance();
30         Calendar calendar2 = calendar;
31         System.out.println(calendar);//直接这样输出的看不懂，java.util.GregorianCalendar[time=1504450592066,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="GMT+08:00",offset=28800000,dstSavings=0,useDaylight=false,transitions=0,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2017,MONTH=8,WEEK_OF_YEAR=36,WEEK_OF_MONTH=2,DAY_OF_MONTH=3,DAY_OF_YEAR=246,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MONTH=1,AM_PM=1,HOUR=10,HOUR_OF_DAY=22,MINUTE=56,SECOND=32,MILLISECOND=66,ZONE_OFFSET=28800000,DST_OFFSET=0]
32
33         //获得date对象
34         date = calendar.getTime();
35
36         //将date中时间设置给calendar
37         calendar.setTime(date);
38
39         //获取
40         calendar.get(Calendar.YEAR);
41
42         //设置
43         calendar.set(Calendar.MONTH, 0);
44
45         //增加
46         calendar.add(Calendar.DAY_OF_YEAR, 10);
47
48         //指定日历字段可能拥有的最大值。在此句中指当前月份的最大天数。
49         calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
50
51
52
53         //boolean类型，判断calendar1的时间是否在calendar2之后
54         calendar.after(calendar2);
55
56         //获得毫秒值，返回long类型
57         calendar.getTimeInMillis();
58
59
60     }
61
62 }