Calender

import java.util.Calendar;
public class CalenderTs {
    public static void main(String[] args) {
        Calendar c = Calendar.getInstance();
        int y = c.get(Calendar.YEAR);
        System.out.println(y);
        int m = c.get(Calendar.MONTH) + 1;
        System.out.println(m);
        int d = c.get(Calendar.DAY_OF_MONTH);
        System.out.println(d);
        int w = c.get(Calendar.DAY_OF_WEEK);
        System.out.println(w);
        int hh = c.get(Calendar.HOUR_OF_DAY);
        System.out.println(hh);
        int mm = c.get(Calendar.MINUTE);
        System.out.println(mm);
        int ss = c.get(Calendar.SECOND);
        System.out.println(ss);
        int ms = c.get(Calendar.MILLISECOND);
        System.out.println(y + "-" + m + "-" + d + " " + w + " " + hh + ":" + mm + ":" + ss + "." + ms);
    }
}

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class CalenderDemo {
    public static void main(String[] args) {
        // 当前时间
        Calendar c = Calendar.getInstance();
        System.out.println(c);
        // 清除所有
        c.clear();
        // 设置年月日时分秒
        c.set(2019, 10 /* 11月 */, 20, 8, 15, 0);
        // 加5天并减去两小时
        c.add(Calendar.DAY_OF_MONTH, 5);
        c.add(Calendar.HOUR_OF_DAY, -2);
        // 显示时间
        var sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date d = c.getTime();
        System.out.println(sdf.format(d));
    }
}

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
public class LocalDateTimeDemo {
    public static void main(String[] args) {
        //当前日期
        LocalDate d = LocalDate.now();
        //当前时间
        LocalTime t = LocalTime.now();
        //当前日期和时间
        LocalDateTime dt = LocalDateTime.now();
        System.out.println(d);
        System.out.println(t);
        System.out.println(dt);
    }
}

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class DateTimeFormatterDemo {
    public static void main(String[] args) {
        //自定义格式化时间
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
        System.out.println(dtf.format(LocalDateTime.now()));
        //用自定义格式解析
        LocalDateTime dt2 = LocalDateTime.parse("2019/11/30 15:16:17", dtf);
        System.out.println(dt2);
    }
}

import java.time.LocalDateTime;
public class LocalDateTimeAddSub {
    public static void main(String[] args) {
        LocalDateTime dt = LocalDateTime.of(2019, 10, 26, 20, 30, 59);
        System.out.println(dt);
        //加5天减三个小时
        LocalDateTime dt2 = dt.plusDays(5).minusHours(3);
        //减一个月
        LocalDateTime dt3 = dt2.minusMinutes(1);
        System.out.println(dt3);
    }
}

import java.time.Instant;
public class InstanceDemo {
    // 获取时间戳
    public static void main(String[] args) {
        Instant now = Instant.now();
        //秒
        System.out.println(now.getEpochSecond());
        //毫秒
        System.out.println(now.toEpochMilli());
    }
}