JDK8中更新的日期时间API

一 . JDK8中加入了几种新的日期时间API

①.LocalDateTime , LocalDate , LocalTime 三者

②.DateTimeFormatter

//LocalDateTime , LocalDate , LocalTime 三者的使用
    //类似于Calendar
    @Test
    public void Test1(){
        //now()
        LocalDate localDate = LocalDate.now();
        LocalTime localTime = LocalTime.now();
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println(localDate); //2021-02-02
        System.out.println(localTime);//14:53:20.995
        System.out.println(localDateTime);//2021-02-02T14:53:20.995

        //of():设置指定的年,月,日,时,分,秒 (没有偏移量)
        LocalDateTime dateTime = LocalDateTime.of(2019, 12, 21, 11, 59, 59);
        System.out.println(dateTime);

        //getXxx()
        System.out.println(localDateTime.getDayOfMonth());
        System.out.println(localDateTime.getDayOfWeek());
        System.out.println(localDateTime.getDayOfYear());
        System.out.println(localDateTime.getMonthValue());//第几月

        //不可变性
        //withXxx():设置相关属性
        LocalDate localDate1 = localDate.withDayOfMonth(22);
        System.out.println(localDate);
        System.out.println(localDate1);

        //plus() : 加
        LocalDateTime localDateTime1 = localDateTime.plusMonths(3);
        System.out.println(localDateTime);
        System.out.println(localDateTime1);

    }


    @Test
    public void Test2(){

        //DateTimeFormatter 相当于 SimpleDateFormat
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd hh-mm-ss");
        String format = dateTimeFormatter.format(LocalDateTime.now());
        System.out.println(format);
    }

二. Instant