Read Day6 30 minutes before going to bed every day_ Day6_ Date_ Calendar_ LocalDate_ TimeStamp_ LocalTime

1. Date introduction

stay Java in The time origin is set to The time zone of the prime meridian 1970 year 1 month 1 Midnight of the day . From the origin , Every day according to 86400 Seconds forward or back .Java Get time in API Yes Date class ,System.currentTimeMillis(),Timestamp,LocalDate,LocalTime, Let's make an introduction .

• Date format settings are DateFormat Subclasses of SimpleDateFormat Set it up , Such as new SimpleDateFormat(“yyyy-MM-dd HH:mm:ss”)

2. util Under the Date class

• The acquisition time is milliseconds , You can follow the format you need , Output after turning , use SimpleDateFormat() Class to format .

//1. util Under the  Date  class 
Date date = new Date();
long time = date.getTime();
// Date formatting , The format is ：yyyy-MM-dd HH:mm:ss
// Before formatting ：1651110193459  Formatted results ： 2022-04-28 09:43:13
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")
String resultTime = dateFormat.format(time);
System.out.println("util Under bag Date class " + time);
System.out.println("util Under bag Date class ,format After ：" + resultTime);
// Date resolution 
Date parse = dateFormat.parse("2022-2-1 12:58:36");
System.out.println("parse  Date resolved into ms : " + parse.getTime());

3. System The way to go

//2. System The way to go ,
// * @return the difference, measured in milliseconds, between
// * the current time and midnight, January 1, 1970 UTC.
// * @see java.util.Date
// */
// millisecond

long timeMillis = System.currentTimeMillis();
// nanosecond 
long nanoTime = System.nanoTime();
System.out.println("System.currentTimeMillis() Get date ："+ timeMillis);
String timeMillisFormat = dateFormat.format(timeMillis);
System.out.println("timeMillisFormat After ：" + timeMillisFormat);
System.out.println("nanoTime  nanosecond ：" + nanoTime);

4. Timestamp（ Belong to sql package ） Is used to util The time obtained is converted to Sql Time that can be stored , And java.sql.Date Class functions are similar to . The former shows the date , Minutes and seconds , The latter only shows the date .

//3. Timestamp, It is specially used for the date format stored in the database , Get the date in the system ,
// On initialization , The time parameter needs to be passed in 
// Specific date , Hours, minutes and seconds can be displayed 
Timestamp timestamp = new Timestamp(new Date().getTime());
System.out.println(" be used for sql Of timeStamp timestamp ：" + timestamp);
// No display   Minutes and seconds , Only the date of the year is displayed 
java.sql.Date date1 = new java.sql.Date(new Date().getTime());
System.out.println("java.sql.Date : " + date1);

5. Calendar

 // 4. Calendar
 Calendar calendar = new GregorianCalendar();
 Date time2 = calendar.getTime();
 System.out.println("Calendar Medium time2 " + time2);
 Instant now = Instant.now();
 System.out.println("Instant " + now);

6.LocalDate & LocalTime（LocalDate There are some ways getDayOfMonth();getDayOfWeek();getDayOfYear();LocalTime Method ：getMinute();getHour();）

 /** * LocalDate  Get local date , Specific date  * LocalTime  Get local date , Minutes and seconds  */
 //localDate  The purpose of the method in , Get today is the day of the year , The day in mid January , The day of the week 
 LocalDate now1 = LocalDate.now();
 System.out.println("LocalDate " + now1);
 int dayOfMonth = now1.getDayOfMonth();
 System.out.println("dayOfMonth "+ dayOfMonth);
 DayOfWeek dayOfWeek = now1.getDayOfWeek();
 System.out.println("DayOfWeek " + dayOfWeek);
 int dayOfYear = now1.getDayOfYear();
 System.out.println("dayOfYear " + dayOfYear);
 LocalTime now2 = LocalTime.now();
 System.out.println("LocalTime " + now2);
 int minute = now2.getMinute();
 System.out.println("minute "+minute);
 int hour = now2.getHour();
 System.out.println("hour " + hour);
// Time   Add   date 
LocalDateTime now3 = LocalDateTime.now();
System.out.println("LocalDateTime "+now3);

7. The second method of date formatting ： DateTimeFormatter

// Date formatting  DateTimeFormatter
// Date formatting  DateTimeFormatter
DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String format = dateTimeFormatter.format(dateTime);
System.out.println("DateTimeFormatter ：" + format);
// Date resolution 
TemporalAccessor parse1 = dateTimeFormatter.parse("2021-05-04 07:56:24");
System.out.println("TemporalAccessor " +parse1 );

Full code display

import java.sql.Timestamp;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.DayOfWeek;
import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalTime;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

/** * @Author Janson * @Date 2022/4/28 9:18 * @Version 1.0 */
public class Day6_Date_Calendar_Time_TimeStamp {
    
    public static void main(String[] args) throws ParseException {
    
        //1. util Under the  Date  class 
        Date date = new Date();
        long time = date.getTime();
        // Date formatting , The format is ：yyyy-MM-dd HH:mm:ss
        // Before formatting ：1651110193459  Formatted results ： 2022-04-28 09:43:13
        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String resultTime = dateFormat.format(time);
        System.out.println("util Under bag Date class " + time);
        System.out.println("util Under bag Date class ,format After ：" + resultTime);
        // Date resolution 
        Date parse = dateFormat.parse("2022-2-1 12:58:36");
        System.out.println("parse  Date resolved into ms : " + parse.getTime());

        //2. System  The way to go ,
        // * @return the difference, measured in milliseconds, between
        // * the current time and midnight, January 1, 1970 UTC.
        // * @see java.util.Date
        // */
        // millisecond 
        long timeMillis = System.currentTimeMillis();
        // nanosecond 
        long nanoTime = System.nanoTime();
        System.out.println("System.currentTimeMillis() Get date ："+ timeMillis);
        String timeMillisFormat = dateFormat.format(timeMillis);
        System.out.println("timeMillisFormat After ：" + timeMillisFormat);
        System.out.println("nanoTime  nanosecond ：" + nanoTime);

        //3. Timestamp, It is specially used for the date format stored in the database , Get the date in the system ,
        // On initialization , The time parameter needs to be passed in 

        // Specific date , Hours, minutes and seconds can be displayed 
        Timestamp timestamp = new Timestamp(new Date().getTime());
        System.out.println(" be used for sql Of timeStamp timestamp ：" + timestamp);
        // No display   Minutes and seconds , Only the date of the year is displayed 
        java.sql.Date date1 = new java.sql.Date(new Date().getTime());
        System.out.println("java.sql.Date : " + date1);

        // 4. Calendar
        Calendar calendar = new GregorianCalendar();
        Date time2 = calendar.getTime();
        System.out.println("Calendar Medium time2 " + time2);

        Instant now = Instant.now();
        System.out.println("Instant " + now);

        /** * LocalDate  Get local date , Specific date  * LocalTime  Get local date , Minutes and seconds  */
        //localDate  The purpose of the method in , Get today is the day of the year , The day in mid January , The day of the week 
        LocalDate now1 = LocalDate.now();
        System.out.println("LocalDate " + now1);
        int dayOfMonth = now1.getDayOfMonth();
        System.out.println("dayOfMonth "+ dayOfMonth);

        DayOfWeek dayOfWeek = now1.getDayOfWeek();
        System.out.println("DayOfWeek " + dayOfWeek);

        int dayOfYear = now1.getDayOfYear();
        System.out.println("dayOfYear " + dayOfYear);

        LocalTime now2 = LocalTime.now();
        System.out.println("LocalTime " + now2);
        int minute = now2.getMinute();
        System.out.println("minute "+minute);
        int hour = now2.getHour();
        System.out.println("hour " + hour);


    }
}