Java在线运行

版本:
运行结果
教程手册
代码仓库
极速运行
终端运行
图形+终端

                        
以下是用户最新保存的代码
冒泡排序和选择排序 发布于:2023-09-22 09:24 百鸡百钱问题 发布于:2023-09-21 23:04 this is 选择排序 发布于:2023-09-21 21:52 this is 冒泡排序 发布于:2023-09-21 21:50 这是选择排序 发布于:2023-09-21 21:02 这是冒泡排序 发布于:2023-09-21 21:01 利用蛮力法解决百鸡百钱问题: 百钱百鸡问题是一道数学题,出自《张邱建算经》, 问题描述如下:“鸡翁一,值钱五;鸡母一,值钱三;鸡雏一,值钱一;百钱买百鸡,则翁、母、雏各几何? 发布于:2023-09-21 20:46 百钱百鸡问题是一道数学题,出自《张邱建算经》,问题描述如下:“鸡翁一,值钱五;鸡母一,值钱三;鸡雏一,值钱一;百钱买百鸡,则翁、母、雏各几何? 发布于:2023-09-21 20:46 产需对齐计算 发布于:2023-09-22 12:54 百钱白鸡问题 发布于:2023-09-21 13:45 选择排序、 发布于:2023-09-20 23:49 选择排序-20052244 发布于:2023-09-20 21:36 百钱百鸡nn 发布于:2023-09-20 21:23 选择排序算法 发布于:2023-09-20 21:14 选择排序测试 发布于:2023-09-20 21:07 选择排序。 发布于:2023-09-20 21:15 寻找数组中的最大值 发布于:2023-09-20 20:54 冒泡排序。 发布于:2023-09-20 21:15 冒泡排序测试 发布于:2023-09-20 20:31 冒泡排序法 发布于:2023-09-20 20:21 20230920-冒泡排序 发布于:2023-09-20 20:26 个位数比百位数大,百位数比十位数大,各数之和等于各数之积,求这个百位数 发布于:2023-09-20 20:15 冒泡排序456321-20052244SQ 发布于:2023-09-20 20:33 冒泡排序432156 发布于:2023-09-20 20:30 有一个三位数,个位数字比百位数字大 发布于:2023-09-20 20:06 搜索小于100,且能被3整除的数 发布于:2023-09-20 19:47 1-10能被3整除 发布于:2023-09-20 19:46 找出能被3整除的数 发布于:2023-09-20 19:44 1-10被3整除的数 发布于:2023-09-20 19:43 抽象加接口 发布于:2023-09-20 16:11 接口Java 发布于:2023-09-20 16:17 定义接口 interface 发布于:2023-09-20 15:27 BOLOOOD 9.20 2.0版本 发布于:2023-09-20 14:53 --- BOLOOL JK 9.20 发布于:2023-09-20 12:28 代码实现选择排序 发布于:2023-09-19 22:13 选择排序。 发布于:2023-09-19 16:50 选择排序算法 发布于:2023-09-19 16:50 冒泡排序算法 发布于:2023-09-19 16:49 冒泡排序算法&&选择排序算法 发布于:2023-09-19 16:50 不完整版对象(待修改)9.19 发布于:2023-09-19 15:27 9.18 算法时间 发布于:2023-09-18 15:18 数组算法课 发布于:2023-09-18 15:16 时间复杂性 发布于:2023-09-18 09:51 对象2023916 发布于:2023-09-16 13:58 请说出你的数字 发布于:2023-09-15 19:43 public class Main { public static void main(String[] args) { String formula = "2*x^2 + 3*x + 4"; Expression expression = new Expression(formula); System.out.println("Formula: " + formula); System.out.println("Parsed expression: " + expression.toString()); } } 发布于:2023-09-15 17:09 mh和zzj 发布于:2023-09-13 16:22 多态的实列 发布于:2023-09-13 15:06 多态的例子 发布于:2023-09-13 15:04 多态编程xx 发布于:2023-09-13 14:55 [更多]
显示目录

Java 8 – Convert Date to LocalDate and LocalDateTime



The java.util.Date has no concept of time zone, and only represents the number of seconds passed since the Unix epoch time – 1970-01-01T00:00:00Z (midnight at the start of January 1, 1970 GMT/UTC)

Note
The new Java 8 java.time.Instant is the equivalent class to the classic java.util.Date

1. Date -> java.time

The idea for the date conversion :

Date -> Instant + System default time zone = LocalDate
Date -> Instant + System default time zone = LocalDateTime
Date -> Instant + System default time zone = ZonedDateTime

This example shows you how to convert java.util.Date to the new Java 8 Date APIs – LocalDate, LocalDateTime and ZonedDateTime

DateToJavaTime.java

package com.mkyong.java8;

import java.time.*;
import java.util.Date;

public class DateToJavaTime {

    public static void main(String[] args) {

        //Asia/Kuala_Lumpur +8
        ZoneId defaultZoneId = ZoneId.systemDefault();
        System.out.println("System Default TimeZone : " + defaultZoneId);

        //toString() append +8 automatically.
        Date date = new Date();
        System.out.println("date : " + date);

        //1. Convert Date -> Instant
        Instant instant = date.toInstant();
        System.out.println("instant : " + instant); //Zone : UTC+0

        //2. Instant + system default time zone + toLocalDate() = LocalDate
        LocalDate localDate = instant.atZone(defaultZoneId).toLocalDate();
        System.out.println("localDate : " + localDate);

        //3. Instant + system default time zone + toLocalDateTime() = LocalDateTime
        LocalDateTime localDateTime = instant.atZone(defaultZoneId).toLocalDateTime();
        System.out.println("localDateTime : " + localDateTime);

        //4. Instant + system default time zone = ZonedDateTime
        ZonedDateTime zonedDateTime = instant.atZone(defaultZoneId);
        System.out.println("zonedDateTime : " + zonedDateTime);

    }

}

Output

System Default TimeZone : Asia/Kuala_Lumpur

date : Fri Aug 19 21:46:31 MYT 2016
instant : 2016-08-19T13:46:31.981Z

localDate : 2016-08-19
localDateTime : 2016-08-19T21:46:31.981
zonedDateTime : 2016-08-19T21:46:31.981+08:00[Asia/Kuala_Lumpur]

2. Explanation – Q&A

2.1 Question : If Date has no concept of time zone, why the time zone will be displayed while we print out the Date object? For example :

//Fri Aug 19 11:52:06 MYT 2016
System.out.println(new Date()); //MYT = my system default time zone

Answer : Check the java.uti.Date.toString() source code, if you print out the Date object, the system default time zone will be appended and display together.

java.util.Date

public String toString() {

        //...omitted...

        TimeZone zi = date.getZone();
        if (zi != null) {
            sb.append(zi.getDisplayName(date.isDaylightTime(), TimeZone.SHORT, Locale.US)); // zzz
        } else {
            sb.append("GMT");
        }
        sb.append(' ').append(date.getYear());  // yyyy
        return sb.toString();
}

Note
This behavior is a design flaw since JDK1.1, it makes a lot of confusion. Again, the java.util.Date doesn’t store any time zone info, but if you print it out, the system default time zone will be displayed together.

2.2 Question : For the Date conversion, why we need to add a system default time zone for java.time.instant?
Answer : Refer to the above 2.1 Q&A. Review another example :

1. Date = 19/08/2016T10:00:00
2. System default time zone = +08:00 [Asia/Kuala_Lumpur]
3. Date (Print) = 19/08/2016T10:00:00+08:00 = 19/08/2016T18:00:00

The goal of the conversion is make sure both print Date and print LocalDate will generates the same output.

// Assume 19/08/2016T10:00:00 = 1000
// System default time zone = +8

1. Date (1000) -> Print Date (1000) = 1000+08:00  
// we always see "1000+08:00" (but the Date is still 1000)

2. Date (1000) -> Instant (1000)
// instant has no time zone or zero offset (UTC+0/Z)

3. Instant(1000) -> LocalDate(1000) -> Print LocalDate(1000) = 1000
// The result is "1000", different with print date!

4. LocalDate(1000) + 08:00 -> LocalDate(1000+08:00)
// add default time zone +8

5. Print LocalDate(1000+08:00) = 1000+08:00

3. java.time -> Date

This example shows you how to convert LocalDate, LocalDateTime and ZonedDateTime back to the classic java.util.Date

JavaTimeToDate.java

package com.mkyong.java8;

import java.time.*;
import java.util.Date;

public class JavaTimeToDate {

    public static void main(String[] args) {

        //Asia/Kuala_Lumpur +8
        ZoneId defaultZoneId = ZoneId.systemDefault();
        System.out.println("System Default TimeZone : " + defaultZoneId);

        LocalDate localDate = LocalDate.of(2016, 8, 19);
        Date date = Date.from(localDate.atStartOfDay(defaultZoneId).toInstant());
        System.out.println("\n1. LocalDate -> Date");
        System.out.println("localDate : " + localDate);
        System.out.println("date : " + date);

        LocalDateTime localDateTime = LocalDateTime.of(2016,8,19,21,46,31);
        Date date2 = Date.from(localDateTime.atZone(defaultZoneId).toInstant());
        System.out.println("\n2. LocalDateTime -> Date");
        System.out.println("localDateTime : " + localDateTime);
        System.out.println("date2 : " + date2);

        ZonedDateTime zonedDateTime = localDateTime.atZone(defaultZoneId);
        Date date3 = Date.from(zonedDateTime.toInstant());
        System.out.println("\n3. ZonedDateTime -> Date");
        System.out.println("zonedDateTime : " + zonedDateTime);
        System.out.println("date3 : " + date3);

    }

}

Output

System Default TimeZone : Asia/Kuala_Lumpur

1. LocalDate -> Date
localDate : 2016-08-19
date : Fri Aug 19 00:00:00 MYT 2016

2. LocalDateTime -> Date
localDateTime : 2016-08-19T21:46:31
date2 : Fri Aug 19 21:46:31 MYT 2016

3. ZonedDateTime -> Date
zonedDateTime : 2016-08-19T21:46:31+08:00[Asia/Kuala_Lumpur]
date3 : Fri Aug 19 21:46:31 MYT 2016

References

  1. JSR 310: Date and Time API
  2. Unix time
  3. Instant JavaDoc
  4. Date JavaDoc
  5. Java – Convert date and time between timezone
由JSRUN为你提供的Java在线运行、在线编译工具
        JSRUN提供的Java 在线运行,Java 在线运行工具,基于linux操作系统环境提供线上编译和线上运行,具有运行快速,运行结果与常用开发、生产环境保持一致的特点。