1. Date and time AP test before jdk8
1. currentTimeMillis () in the
system
class
2. java.util.Date and Java.sql.Date 3. SimpleDateFormat class 4.Calendar class
1.1. CurrentTimeMillis (): returns the current computer time, the time format is the current computer time and GMT time (Greenwich Mean Time), to obtain the milliseconds starting on January 1, 1970 0: 00: 00: 00 number
1.2, the string 2019-09-08 is converted to java.sql.Date
public void testExer() throws ParseException {
String brith = "2019-09-08";
SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd");
Date date = sdf1.parse(brith);
System.out.println(date);
java.sql.Date brithDate = new java.sql.Date(date.getTime());
System.out.println(brithDate);
}
1.3, the use of SimpleDateFormat: SimpleDateFormat class for date format analysis
① Two operations
1.1 formatting: date—> string
1.2 parsing: string—> date
② The instantiation of SimpleDateFormat
public void test() throws ParseException {
//实例化
SimpleDateFormat sdf = new SimpleDateFormat();
//格式化：日期 --->字符串
Date date =new Date();
System.out.println(date);
String format = sdf.format(date);
System.out.println(format);
// 解析:字符串--->日期
String str = "20-3-25 下午10:02";
Date date1 = sdf.parse(str);
System.out.println(date1);
System.out.println("**********************************");
SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd");
String format1 = sdf1.format(date);
System.out.println(format1);
}
1.4. Use of Calendar class (abstract class)
① Instantiation
// Method 1: Create a subclass (GregorianCalendar) object
// Method 2: Call its static method getInstance ();
Calendar calendar = Calendar.getInstance();
System.out.println(calendar.getClass());
② Common methods
//get() 获取当前日期的年月日
int days = calendar.get(calendar.DAY_OF_MONTH);
System.out.println(days);
//set() 设置当前日期的年月日
calendar.set(calendar.DAY_OF_MONTH,22);
days = calendar.get(calendar.DAY_OF_MONTH);
System.out.println(days);
//add()给当前日期添加年月日的时间
calendar.add(calendar.DAY_OF_MONTH,3);
days = calendar.get(calendar.DAY_OF_MONTH);
System.out.println(days);
calendar.add(calendar.DAY_OF_MONTH,-3);
days = calendar.get(calendar.DAY_OF_MONTH);
System.out.println(days);
//getTime()获取当前时间的时间戳 日历类-- date类
Date date = calendar.getTime();
System.out.println(date);
//setTime() date --- 日历类
Date date1 = new Date();
calendar.setTime(date1);
days = calendar.get(calendar.DAY_OF_MONTH);
System.out.println(days);
2. API test of jdk8 date and time
2.1, LocalDate, LocalTime, LocalDateTime use local date and time
Note:
1. LocalDateTime is used more frequently than LocalDate and LocalTime
2. Similar to Calender
public void testDate(){//已过期 deprecated 偏移量的问题
Date date = new Date(2020 - 1900,9 - 1,8);
System.out.println(date);
}
@Test
public void test(){
//实例化
//now():获取当前的 日期 时间 日期+时间
LocalDate localDate = LocalDate.now();
LocalTime localTime = LocalTime.now();
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println(localDate);
System.out.println(localTime);
System.out.println(localDateTime);
//of():设置指定的年月日时分秒，没有偏移量
// LocalDateTime localDateTime1 = LocalDateTime.of(2020,10,26);
// System.out.println(localDateTime1);
//getXXX():获取属性值
System.out.println(localDateTime.getDayOfMonth());
System.out.println(localDateTime.getDayOfWeek());
System.out.println(localDateTime.getMonth());
System.out.println(localDateTime.getMonthValue());
System.out.println(localDateTime.getMinute());
//有返回值，不用修改原来的值，体现不可变性,修改值
//with()：设置相关属性
LocalDateTime localDateTime1 = localDateTime.withDayOfMonth(22);
System.out.println(localDateTime1);
LocalDateTime localDateTime2 = localDateTime.withHour(4);
System.out.println(localDateTime);
System.out.println(localDateTime2);
//不可变性，plus添加相关时间
LocalDateTime localDateTime3 = localDateTime.plusMonths(3);
System.out.println(localDateTime);
System.out.println(localDateTime3);
//原来的值不变，新增新的值 minus 减去相应的时间
LocalDateTime localDateTime4 = localDateTime.minusDays(6);
System.out.println(localDateTime);
System.out.println(localDateTime4);
}
2.2. Instant class: An instantaneous point in time, which may be used to record the event timestamp in the application.
1. In Java, starting from 0:00:00 on January 1, 1970, in milliseconds.
2. Similar to java.util.Date class
@Test
public void test1(){
//now():获取本初子午线对应的标准时间
Instant instant = Instant.now();
System.out.println(instant);
//添加时间的偏移量
OffsetDateTime offsetDateTime = instant.atOffset(ZoneOffset.ofHours(8));
System.out.println(offsetDateTime);
//获取子1970年1月1日0时0分0秒(UTC)开始的毫秒数
//toEpochMilli()
long mill = instant.toEpochMilli();
System.out.println(mill);
//通过给定的毫秒数，获取Instant实例 -->date类中的getTime()
Instant instant1 = Instant.ofEpochMilli(1585193930875L);
System.out.println(instant1);
}
2.3, DateTimeFormatter: format or parse date and time similar to simpleDateFormat
Method 1: Predefined standard format
/*
三种方式
1.ISO_LOCAL_DATE_TIME
2.ISO_LOCAL_DATE
3.ISO_LOCAL_TIME
*/
DateTimeFormatter formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
//格式化：日期--->字符串
LocalDateTime localDateTime = LocalDateTime.now();
String str = formatter.format(localDateTime);
System.out.println(localDateTime);
System.out.println(str);//20-3-26 下午8:05
//解析：字符串-->日期
TemporalAccessor parse = formatter.parse("2020-03-26T19:58:57.398");
System.out.println(parse);
Method 2: Localization-related formats: such as ofLocalizedDateTime (), FormatStyle.LONG / FormatStyle.MEDIUM / FormatStyle.SHORT: applicable to LocalDateTime
DateTimeFormatter formatter1 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT);
// DateTimeFormatter formatter2 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM);
// DateTimeFormatter formatter3 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG);
//格式化
String str2 = formatter1.format(localDateTime);
System.out.println(str2);
//本地化相关方法 如：ofLocalizedDate()
// FormatStyle.FULL/ FormatStyle.LONG / FormatStyle.MEDIUM /FormatStyle.SHORT:适用于LocalDate
DateTimeFormatter formatter2 = DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL);
String format = formatter2.format(LocalDate.now());
System.out.println(format);//2020年3月26日 星期四
Focus: Method 3: Customized format such as ofPattern ("yyyy-MM-dd hh: mm: ss")
DateTimeFormatter formatter3 = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
//格式化
String format1 = formatter3.format(LocalDateTime.now());
System.out.println(format1);
//解析
TemporalAccessor parse1 = formatter3.parse("2019-03-26 08:14:19");
System.out.println(parse1);
One of the commonly used classes in Java-String, StringBuffer, StringBuilder
https://blog.csdn.net/weixin_43244120/article/details/105187804
Three of the commonly used classes of Java-other classes (interfaces)
https://blog.csdn.net/weixin_43244120/article/details/105189069
