Java:日期-时间

JDK1.8 以前版本

import java.util.Date;

public class Driver {
    public static void main(String[] args) {

        //获取系统剩余的内存空间
        long begin1 = Runtime.getRuntime().freeMemory();
        //获取系统的当前时间
        long start01 = System.currentTimeMillis();



        //获取系统当前时间戳：
        System.out.println(System.currentTimeMillis());
        //获取当前时间：
        Date now=new Date();
        System.out.println(now);
        //把Date转化为1ong：
        long t=now.getTime();
        System.out.println(t);
        //把1ong转化为Date：
        System.out.println(new Date(t));





        //获取系统剩余的内存空间
        long end2 = Runtime.getRuntime().freeMemory();
        //获取系统的当前时间  单位是毫秒
        long finish02 = System.currentTimeMillis();
        System.out.println("本程序占用内存:" + (begin1 - end2));
        System.out.println("本程序占用时间:" + (finish02 - start01));
    }
}









import java.util.Date;

public class Driver {
    public static void main(String[] args) {

        //获取系统剩余的内存空间
        long begin1 = Runtime.getRuntime().freeMemory();
        //获取系统的当前时间
        long start01 = System.currentTimeMillis();


        //获取当前时间：
        Date now=new Date();
        //以当前时区打印日期时间：
        System.out.println(now.toString());
        //以GMg+00：00时区打印日期时间：
        System.out.println(now.toGMTString());
        //以当前时区+当前Locale打印日期时间：
        System.out.println(now.toLocaleString());


        System.out.println("\t\t");
        //获取系统剩余的内存空间
        long end2 = Runtime.getRuntime().freeMemory();
        //获取系统的当前时间  单位是毫秒
        long finish02 = System.currentTimeMillis();
        System.out.println("本程序占用内存:" + (begin1 - end2));
        System.out.println("本程序占用时间:" + (finish02 - start01));
    }
}






import java.text.SimpleDateFormat;
import java.util.Date;

public class Driver {
    public static void main(String[] args) {

        //获取系统剩余的内存空间
        long begin1 = Runtime.getRuntime().freeMemory();
        //获取系统的当前时间
        long start01 = System.currentTimeMillis();


        //获取当前时间：
        Date now=new Date();
//        SimpleDateFormat simpleDateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss z");
        SimpleDateFormat simpleDateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
        System.out.println(simpleDateFormat.format(now));

        System.out.println("\t\t");
        //获取系统剩余的内存空间
        long end2 = Runtime.getRuntime().freeMemory();
        //获取系统的当前时间  单位是毫秒
        long finish02 = System.currentTimeMillis();
        System.out.println("本程序占用内存:" + (begin1 - end2));
        System.out.println("本程序占用时间:" + (finish02 - start01));
    }
}

JDK1.8及其以后的版本

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAdjuster;
import java.time.temporal.TemporalAdjusters;

public class Driver {
    public static void main(String[] args) {

        //获取系统剩余的内存空间
        long begin1 = Runtime.getRuntime().freeMemory();
        //获取系统的当前时间
        long start01 = System.currentTimeMillis();


        //当前日期
        LocalDate localDate=LocalDate.now();
        System.out.println(localDate);
        //当前时间
        LocalTime localTime=LocalTime.now();
        System.out.println(localTime);
        //当前日期和时间
        LocalDateTime localDateTime=LocalDateTime.now();
        System.out.println(localDateTime);


        DateTimeFormatter dateTimeFormatter=DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        System.out.println(dateTimeFormatter.format(LocalDateTime.now()));






        LocalDateTime localDateTime1=LocalDateTime.parse("2000-05-06 13:07:59",dateTimeFormatter);
        System.out.println(localDateTime1);


        // 日期和时间运算

        //日期运算
        LocalDate today=LocalDate.now();
        LocalDate after5days=today.plusDays(2);
        System.out.println(today);
        System.out.println(after5days);

        //时间运算
        LocalDateTime now=LocalDateTime.now();
        LocalDateTime before2hours=now.minusHours(3);
        System.out.println(now);
        System.out.println(before2hours);

        // 加3个月 减去两周
        LocalDate localDate1=today.plusMonths(3).minusWeeks(2);
        System.out.println(localDate1);

        //本月第一天
        LocalDate firstDay=LocalDate.now().withDayOfMonth(1);
        System.out.println(firstDay);


        //把秒和纳秒调整为0
        LocalTime localTime1=LocalTime.now().withSecond(0).minusNanos(0);
        System.out.println(localTime1);

        //本月最后一天
        LocalDate lastDay=LocalDate.now().with(TemporalAdjusters.lastDayOfMonth());
        System.out.println(lastDay);


        //本月第一周日
        LocalDate firstSunday=LocalDate.now().with(TemporalAdjusters.firstInMonth((DayOfWeek.SUNDAY)));
        System.out.println(firstSunday);



        
        System.out.println("\t\t");
        //获取系统剩余的内存空间
        long end2 = Runtime.getRuntime().freeMemory();
        //获取系统的当前时间  单位是毫秒
        long finish02 = System.currentTimeMillis();
        System.out.println("本程序占用内存:" + (begin1 - end2));
        System.out.println("本程序占用时间:" + (finish02 - start01));
    }
}