Java学习之日期操作

一、日期格式化

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateDemo {

    public static void main(String[] args) {
    Date date=new Date();
    
    DateFormat dateFormat=DateFormat.getDateInstance();
    
    System.out.println(dateFormat.format(date));
    
    dateFormat=new SimpleDateFormat("yyyy--MM--dd");
    System.out.println(dateFormat.format(date));
    }
}

自定义格式化SimpleDateFormat字母代表的意义

Letter	Date or Time Component	Presentation	Examples
G	Era designator	Text	AD
y	Year	Year	1996; 96
Y	Week year	Year	2009; 09
M	Month in year (context sensitive)	Month	July; Jul; 07
L	Month in year (standalone form)	Month	July; Jul; 07
w	Week in year	Number	27
W	Week in month	Number	2
D	Day in year	Number	189
d	Day in month	Number	10
F	Day of week in month	Number	2
E	Day name in week	Text	Tuesday; Tue
u	Day number of week (1 = Monday, ..., 7 = Sunday)	Number	1
a	Am/pm marker	Text	PM
H	Hour in day (0-23)	Number	0
k	Hour in day (1-24)	Number	24
K	Hour in am/pm (0-11)	Number	0
h	Hour in am/pm (1-12)	Number	12
m	Minute in hour	Number	30
s	Second in minute	Number	55
S	Millisecond	Number	978
z	Time zone	General time zone	Pacific Standard Time; PST; GMT-08:00
Z	Time zone	RFC 822 time zone	-0800
X	Time zone	ISO 8601 time zone	-08; -0800; -08:00

二、日期字符串转日期对象

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;

public class DateDemo {

    public static void main(String[] args) throws ParseException {
    String strDate="2019/12/30";
    
    DateFormat dateFormat=DateFormat.getDateInstance();
    
    System.out.println(dateFormat.parse(strDate));
    strDate="2019--11--30";
    dateFormat=new SimpleDateFormat("yyyy--MM--dd");
    System.out.println(dateFormat.parse(strDate));
    }
}

 三、日期操作

Date不够国际化已被Calender取代了

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

public class DateDemo {

    public static void main(String[] args) throws ParseException {
 9     //系统默认时间
    Calendar c = Calendar.getInstance();
    //指定时间
    c.set(2019,2,1);//月是从零开始的
    //时间偏移
    c.add(Calendar.DAY_OF_MONTH, -1);
    show(c);

    }

    private static void show(Calendar c) {
    int year = c.get(Calendar.YEAR);
    int month = c.get(Calendar.MONTH) + 1;
    int day = c.get(Calendar.DAY_OF_MONTH);
    int week = c.get(Calendar.DAY_OF_WEEK);
    System.out.println(year + "/" + month + "/" + day+"  "+getWeek(week));
    }
    
    private static String getWeek(int index) {
    String[] week= {"","星期日","星期一","星期二","星期三","星期四","星期五","星期六"};
    return week[index];    
    }
}