第十三章 新特性

13.1 JSR\JCP

JSR是Java Specification Requests的缩写，意思是Java 规范提案。是指向JCP(Java Community Process)提出新增一个标准化技术规范的正式请求。任何人都可以提交JSR，以向Java平台增添新的API和服务。JSR已成为Java界的一个重要标准。

JCP（Java Community Process) 是一个开放的国际组织，主要由Java开发者以及被授权者组成，职能是发展和更新。

2018年5月17日，作为唯一中国代表，阿里巴巴获邀加入[Java]全球管理组织Java Community Process （JCP）的最高执行委员会JCP-EC。此次获得执行委员会席位，让中国企业首次加入到Java全球标准的制定中，更多“中国标准”有望成为全球规范。该席位将于5月24日生效。

13.2 java版本命名

• java 1.0

• java 1.1

• java 1.2 j2se j2me j2ee java 1.5

• java 1.6 java 6.0

• java 7 try with switch String

• java8

  Locale.setDefault(Locale.CHINA);
  
  // java.util.Date
  LocalDate d = LocalDate.now(ZoneId.of("PRC")); // 当前系统的日期
  System.out.println(d);
  System.out.println(d.getDayOfWeek());
  
  // 建立指定的日期及格式化输出效果
  LocalDate birth = LocalDate.of(1985, 3, 16);
  System.out.println(birth.format(DateTimeFormatter.ofPattern("yyyy年MM月dd日")));
  
  // 将一个字符串，按格式化类规则，直接转化为LocalDate
  LocalDate dd = LocalDate.parse("1985-03-05", DateTimeFormatter.ofPattern("yyyy-MM-dd"));
  
  System.out.println(dd);
  
  System.out.println(dd.isLeapYear());
  
  System.out.println(dd.getDayOfWeek());
  
  // 计算两个日期有多少天
  long days = ChronoUnit.DAYS.between(dd, d);
  System.out.println(days);
  
  LocalTime time = LocalTime.now();
  
  System.out.println(time.format(DateTimeFormatter.ofPattern("HH:mm:ss")));
  
  LocalDateTime now = LocalDateTime.now();
  
  String info = now.format(DateTimeFormatter.ofPattern("yyyy年MM月dd日  HH:mm:ss "));
  System.out.println(info);
  
  //java.util.Date 转换为 java8 LocalDateTime
  Date todayDate = new Date();
  LocalDateTime ldt = todayDate.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();
  System.out.println(ldt.format(DateTimeFormatter.ofPattern("yyyy年MM月dd日  HH:mm:ss ")));
  
  //java8 LocalDateTime 转换为 java.util.Date
  Date date = Date.from( ldt.atZone( ZoneId.systemDefault()).toInstant());
  System.out.println(date);
  
  
  

13.3 Java8 日期时间

Instant         时间戳
Duration        持续时间、时间差
LocalDate       只包含日期，比如：2018-09-24
LocalTime       只包含时间，比如：10:32:10
LocalDateTime   包含日期和时间，比如：2018-09-24 10:32:10
Peroid          时间段
ZoneOffset      时区偏移量，比如：+8:00
ZonedDateTime   带时区的日期时间
Clock           时钟，可用于获取当前时间戳
java.time.format.DateTimeFormatter      时间格式化类

/*
 * Copyright (c) 2006, 2021, webrx.cn All rights reserved.
 *
 */
package cn;

import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.Date;

/**
 * 
Project: part13 - Java80
 * 
Powered By webrx
 * 
Created By IntelliJ IDEA On 2021-02-02 14:56:13
 * 
Description :
 *
 * @author webrx [webrx@126.com]
 * @version 1.0
 * @since 15
 */
public class Java81 {
    public static void main(String[] args) {
        //LocalDate
        LocalDate s1 = LocalDate.of(2021,1,5);
        LocalDate s2 = LocalDate.now();
        System.out.println(s1.until(s2,ChronoUnit.DAYS));

        //获取两个日期之间的天数
        Period p = Period.between(s1, s2);
        System.out.println(p.getDays());

        System.out.println(Instant.now().toEpochMilli());
        System.out.println(System.currentTimeMillis());
        System.out.println(new Date().getTime());
        long n = new Date(System.currentTimeMillis()).getTime();
        System.out.println(n);
        System.exit(0);


        //System.out.println(012);
        //System.out.println(030 < 30);
        LocalTime now = LocalTime.now();
        LocalTime aa = LocalTime.of(16, 3);
        Duration duration = Duration.between(aa, now);
        System.out.println(duration.getSeconds());







        //判断指定的月日，是不是日期
        System.out.println(LocalDate.of(2021, 2, 2).equals(LocalDate.now()));
        System.out.println(MonthDay.of(2, 2).equals(MonthDay.now()));
        System.out.println(MonthDay.of(2, 2) == MonthDay.now());


        System.out.println(LocalDate.now().minusDays(5).plusDays(10).format(DateTimeFormatter.ofPattern("yyyy-MM-dd")));

        LocalDate a = LocalDate.of(2000, 1, 6);
        LocalDate b = LocalDate.parse("2021-09-05", DateTimeFormatter.ofPattern("yyyy-MM-dd"));
        System.out.println(a);
        System.out.println(b);
        System.out.println(a.equals(b));
        System.out.println(a.plusDays(100));
        System.out.println(a.plus(100, ChronoUnit.DAYS));
        System.out.println(a.minus(2, ChronoUnit.DAYS));
        System.exit(0);


        LocalDate d = LocalDate.now();
        d = LocalDate.of(2023, 2, 2);
        d = LocalDateTime.now(ZoneId.of("PRC")).toLocalDate();

        d = LocalDate.now(ZoneId.of("PRC"));
        System.out.println(LocalDate.now());
        System.out.println(LocalDate.now().format(DateTimeFormatter.ofPattern("yyyy年MM月dd日")));
        System.out.printf("%tF %1$tT", LocalDateTime.now());
        System.out.println(d.getYear());
        Month m = d.getMonth();
        System.out.println(m.getValue());
        System.out.println(d.getMonth().plus(3).getValue());
        System.out.println(d.getMonth().plus(-3).getValue());
        System.out.println(d.getMonthValue());
        System.out.println(d.getDayOfMonth());
    }
}

13.4 java12 switch expression

/*
 * Copyright (c) 2006, 2021, webrx.cn All rights reserved.
 *
 */
package cn;


import static cn.exam.Fruit.*;

/**
 * 
Project: part13 - Java10
 * 
Powered By webrx
 * 
Created By IntelliJ IDEA On 2021-02-04 09:24:54
 * 
Description :
 *
 * @author webrx [webrx@126.com]
 * @version 1.0
 * @since 15
 */

public class Java12 {
    public static void main(String[] args) {
        var f = PAPAYA;
        var price = switch (f) {
            case APPLE,GRAPE -> 5;
            case ORAGE, MONGO -> 10;
            default -> 6;
        };
        System.out.println(price);

    }

}