java基础day04-常用API,包装类

常用API,包装类

• ①Data
• ②SimpleDataFormat
• ③Calendar
• ①概述LocalTime/LocalDate/LocalDateTime
• • 1.localDate
  • 2.localTime
  • 3.localDateTime
  • 4.updateTime
• ②instant
• ③DateTimeFormatter
• ④Duration/Period
• ⑤ChronoUnit

一.日期与时间

• ①Data
• ②SimpleDataFormat
• ③Calendar
• ①概述LocalTime/LocalDate/LocalDateTime
• • 1.localDate
  • 2.localTime
  • 3.localDateTime
  • 4.updateTime
• ②instant
• ③DateTimeFormatter
• ④Duration/Period
• ⑤ChronoUnit

①Data

②SimpleDataFormat

③Calendar

// 1、拿到系统此刻日历对象
        Calendar cal = Calendar.getInstance();
        System.out.println(cal);

        // 2、获取日历的信息:public int get(int field)：取日期中的某个字段信息。
        int year = cal.get(Calendar.YEAR);
        System.out.println(year);

        int mm = cal.get(Calendar.MONTH) + 1;
        System.out.println(mm);

        int days = cal.get(Calendar.DAY_OF_YEAR) ;
        System.out.println(days);

        // 3、public void set(int field,int value)：修改日历的某个字段信息。
        // cal.set(Calendar.HOUR , 12);
        // System.out.println(cal);

        // 4.public void add(int field,int amount)：为某个字段增加/减少指定的值
        // 请问64天后是什么时间
        cal.add(Calendar.DAY_OF_YEAR , 64);
        cal.add(Calendar.MINUTE , 59);

        //  5.public final Date getTime(): 拿到此刻日期对象。
        Date d = cal.getTime();
        System.out.println(d);

        //  6.public long getTimeInMillis(): 拿到此刻时间毫秒值
        long time = cal.getTimeInMillis();
        System.out.println(time);

二.jdk8新增日期类

• ①Data
• ②SimpleDataFormat
• ③Calendar
• ①概述LocalTime/LocalDate/LocalDateTime
• • 1.localDate
  • 2.localTime
  • 3.localDateTime
  • 4.updateTime
• ②instant
• ③DateTimeFormatter
• ④Duration/Period
• ⑤ChronoUnit

①概述LocalTime/LocalDate/LocalDateTime

1.localDate

package com.itheima.d4_jdk8_time;
import java.time.LocalDate;
import java.time.Month;

public class Demo01LocalDate {
    public static void main(String[] args) {
        // 1、获取本地日期对象。
        LocalDate nowDate = LocalDate.now();
        System.out.println("今天的日期：" + nowDate);//今天的日期：

        int year = nowDate.getYear();
        System.out.println("year：" + year);


        int month = nowDate.getMonthValue();
        System.out.println("month：" + month);

        int day = nowDate.getDayOfMonth();
        System.out.println("day：" + day);

        //当年的第几天
        int dayOfYear = nowDate.getDayOfYear();
        System.out.println("dayOfYear：" + dayOfYear);

        //星期
        System.out.println(nowDate.getDayOfWeek());
        System.out.println(nowDate.getDayOfWeek().getValue());

        //月份
        System.out.println(nowDate.getMonth());//AUGUST
        System.out.println(nowDate.getMonth().getValue());//8

        System.out.println("------------------------");
        LocalDate bt = LocalDate.of(1991, 11, 11);
        System.out.println(bt);//直接传入对应的年月日
        System.out.println(LocalDate.of(1991, Month.NOVEMBER, 11));//相对上面只是把月换成了枚举
    }
}

2.localTime

package com.itheima.d4_jdk8_time;

import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.Month;

public class Demo02LocalTime {
    public static void main(String[] args) {
        // 1、获取本地时间对象。
        LocalTime nowTime = LocalTime.now();
        System.out.println("今天的时间：" + nowTime);//今天的时间：

        int hour = nowTime.getHour();//时
        System.out.println("hour：" + hour);//hour：

        int minute = nowTime.getMinute();//分
        System.out.println("minute：" + minute);//minute：

        int second = nowTime.getSecond();//秒
        System.out.println("second：" + second);//second：

        int nano = nowTime.getNano();//纳秒
        System.out.println("nano：" + nano);//nano：

        System.out.println("-----");
        System.out.println(LocalTime.of(8, 20));//时分
        System.out.println(LocalTime.of(8, 20, 30));//时分秒
        System.out.println(LocalTime.of(8, 20, 30, 150));//时分秒纳秒
        LocalTime mTime = LocalTime.of(8, 20, 30, 150);

        System.out.println("---------------");
        System.out.println(LocalDateTime.of(1991, 11, 11, 8, 20));
        System.out.println(LocalDateTime.of(1991, Month.NOVEMBER, 11, 8, 20));
        System.out.println(LocalDateTime.of(1991, 11, 11, 8, 20, 30));
        System.out.println(LocalDateTime.of(1991, Month.NOVEMBER, 11, 8, 20, 30));
        System.out.println(LocalDateTime.of(1991, 11, 11, 8, 20, 30, 150));
        System.out.println(LocalDateTime.of(1991, Month.NOVEMBER, 11, 8, 20, 30, 150));
    }
}

3.localDateTime

package com.itheima.d4_jdk8_time;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;

public class Demo03LocalDateTime {
    public static void main(String[] args) {
        // 日期 时间
        LocalDateTime nowDateTime = LocalDateTime.now();
        System.out.println("今天是：" + nowDateTime);//今天是：
        System.out.println(nowDateTime.getYear());//年
        System.out.println(nowDateTime.getMonthValue());//月
        System.out.println(nowDateTime.getDayOfMonth());//日
        System.out.println(nowDateTime.getHour());//时
        System.out.println(nowDateTime.getMinute());//分
        System.out.println(nowDateTime.getSecond());//秒
        System.out.println(nowDateTime.getNano());//纳秒
        //日：当年的第几天
        System.out.println("dayOfYear：" + nowDateTime.getDayOfYear());//dayOfYear：249
        //星期
        System.out.println(nowDateTime.getDayOfWeek());//THURSDAY
        System.out.println(nowDateTime.getDayOfWeek().getValue());//4
        //月份
        System.out.println(nowDateTime.getMonth());//SEPTEMBER
        System.out.println(nowDateTime.getMonth().getValue());//9


        LocalDate ld = nowDateTime.toLocalDate();
        System.out.println(ld);

        LocalTime lt = nowDateTime.toLocalTime();
        System.out.println(lt.getHour());
        System.out.println(lt.getMinute());
        System.out.println(lt.getSecond());
    }
}

4.updateTime

package com.itheima.d4_jdk8_time;

import java.time.LocalDate;
import java.time.LocalTime;
import java.time.MonthDay;

public class Demo04UpdateTime {
    public static void main(String[] args) {
        LocalTime nowTime = LocalTime.now();
        System.out.println(nowTime);//当前时间
        System.out.println(nowTime.minusHours(1));//一小时前
        System.out.println(nowTime.minusMinutes(1));//一分钟前
        System.out.println(nowTime.minusSeconds(1));//一秒前
        System.out.println(nowTime.minusNanos(1));//一纳秒前

        System.out.println("----------------");

        System.out.println(nowTime.plusHours(1));//一小时后
        System.out.println(nowTime.plusMinutes(1));//一分钟后
        System.out.println(nowTime.plusSeconds(1));//一秒后
        System.out.println(nowTime.plusNanos(1));//一纳秒后

        System.out.println("------------------");
        // 不可变对象，每次修改产生新对象！
        System.out.println(nowTime);

        System.out.println("---------------");
        LocalDate myDate = LocalDate.of(2018, 9, 5);
        LocalDate nowDate = LocalDate.now();

        System.out.println("今天是2018-09-06吗？ " + nowDate.equals(myDate));//今天是2018-09-06吗？ false
        System.out.println(myDate + "是否在" + nowDate + "之前？ " + myDate.isBefore(nowDate));//2018-09-05是否在2018-09-06之前？ true
        System.out.println(myDate + "是否在" + nowDate + "之后？ " + myDate.isAfter(nowDate));//2018-09-05是否在2018-09-06之后？ false

        System.out.println("---------------------------");
        // 判断今天是否是你的生日
        LocalDate birDate = LocalDate.of(1996, 8, 5);
        LocalDate nowDate1 = LocalDate.now();

        MonthDay birMd = MonthDay.of(birDate.getMonthValue(), birDate.getDayOfMonth());
        MonthDay nowMd = MonthDay.from(nowDate1);

        System.out.println("今天是你的生日吗？ " + birMd.equals(nowMd));//今天是你的生日吗？ false
    }
}

②instant

`package com.itheima.d4_jdk8_time;

import java.time.Instant;
import java.time.LocalDate;
import java.time.ZoneId;
import java.util.Date;

public class Demo05Instant {
public static void main(String[] args) {
// 1、得到一个Instant时间戳对象
Instant instant = Instant.now();
System.out.println(instant);

    // 2、系统此刻的时间戳怎么办？
    Instant instant1 = Instant.now();
    System.out.println(instant1.atZone(ZoneId.systemDefault()));

    // 3、如何去返回Date对象
    Date date = Date.from(instant);
    System.out.println(date);

    Instant i2 = date.toInstant();
    System.out.println(i2);
}

}
`

③DateTimeFormatter

package com.itheima.d4_jdk8_time;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class Demo06DateTimeFormat {
    public static void main(String[] args) {
        // 本地此刻  日期时间 对象
        LocalDateTime ldt = LocalDateTime.now();
        System.out.println(ldt);

        // 解析/格式化器
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss EEE a");
        // 正向格式化
        System.out.println(dtf.format(ldt));
        // 逆向格式化
        System.out.println(ldt.format(dtf));

        // 解析字符串时间
        DateTimeFormatter dtf1 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        // 解析当前字符串时间成为本地日期时间对象
        LocalDateTime ldt1 = LocalDateTime.parse("2019-11-11 11:11:11" ,  dtf1);
        System.out.println(ldt1);
        System.out.println(ldt1.getDayOfYear());
    }
}

④Duration/Period

`package com.itheima.d4_jdk8_time;

import java.time.LocalDate;
import java.time.Period;

public class Demo07Period {
    public static void main(String[] args) {
        // 当前本地 年月日
        LocalDate today = LocalDate.now();
        System.out.println(today);//

        // 生日的 年月日
        LocalDate birthDate = LocalDate.of(1998, 10, 13);
        System.out.println(birthDate);

        Period period = Period.between(birthDate, today);//第二个参数减第一个参数

        System.out.println(period.getYears());
        System.out.println(period.getMonths());
        System.out.println(period.getDays());
    }
}

package com.itheima.d4_jdk8_time;

import java.time.Duration;
import java.time.LocalDateTime;

public class Demo08Duration {
    public static void main(String[] args) {
        // 本地日期时间对象。
        LocalDateTime today = LocalDateTime.now();
        System.out.println(today);

        // 出生的日期时间对象
        LocalDateTime birthDate = LocalDateTime.of(2021,8
                ,06,01,00,00);

        System.out.println(birthDate);

        Duration duration = Duration.between(birthDate,today );//第二个参数减第一个参数

        System.out.println(duration.toDays());//两个时间差的天数
        System.out.println(duration.toHours());//两个时间差的小时数
        System.out.println(duration.toMinutes());//两个时间差的分钟数
        System.out.println(duration.toMillis());//两个时间差的毫秒数
        System.out.println(duration.toNanos());//两个时间差的纳秒数
    }
}

⑤ChronoUnit

package com.itheima.d4_jdk8_time;

import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;

public class Demo09ChronoUnit {
    public static void main(String[] args) {
        // 本地日期时间对象：此刻的
        LocalDateTime today = LocalDateTime.now();
        System.out.println(today);

        // 生日时间
        LocalDateTime birthDate = LocalDateTime.of(1990,10,1,
                10,50,59);
        System.out.println(birthDate);

        System.out.println("相差的年数：" + ChronoUnit.YEARS.between(birthDate, today));
        System.out.println("相差的月数：" + ChronoUnit.MONTHS.between(birthDate, today));
        System.out.println("相差的周数：" + ChronoUnit.WEEKS.between(birthDate, today));
        System.out.println("相差的天数：" + ChronoUnit.DAYS.between(birthDate, today));
        System.out.println("相差的时数：" + ChronoUnit.HOURS.between(birthDate, today));
        System.out.println("相差的分数：" + ChronoUnit.MINUTES.between(birthDate, today));
        System.out.println("相差的秒数：" + ChronoUnit.SECONDS.between(birthDate, today));
        System.out.println("相差的毫秒数：" + ChronoUnit.MILLIS.between(birthDate, today));
        System.out.println("相差的微秒数：" + ChronoUnit.MICROS.between(birthDate, today));
        System.out.println("相差的纳秒数：" + ChronoUnit.NANOS.between(birthDate, today));
        System.out.println("相差的半天数：" + ChronoUnit.HALF_DAYS.between(birthDate, today));
        System.out.println("相差的十年数：" + ChronoUnit.DECADES.between(birthDate, today));
        System.out.println("相差的世纪（百年）数：" + ChronoUnit.CENTURIES.between(birthDate, today));
        System.out.println("相差的千年数：" + ChronoUnit.MILLENNIA.between(birthDate, today));
        System.out.println("相差的纪元数：" + ChronoUnit.ERAS.between(birthDate, today));
    }
}

三.包装类

• ①Data
• ②SimpleDataFormat
• ③Calendar
• ①概述LocalTime/LocalDate/LocalDateTime
• • 1.localDate
  • 2.localTime
  • 3.localDateTime
  • 4.updateTime
• ②instant
• ③DateTimeFormatter
• ④Duration/Period
• ⑤ChronoUnit

package com.itheima.d5_integer;


public class Test {
    public static void main(String[] args) {
        int a = 10;
        Integer a1 = 11;
        Integer a2 = a; // 自动装箱
        System.out.println(a);
        System.out.println(a1);

        Integer it = 100;
        int it1 = it; // 自动拆箱
        System.out.println(it1);

        double db = 99.5;
        Double db2 = db; // 自动装箱了
        double db3 = db2; // 自动拆箱
        System.out.println(db3);

        // int age = null; // 报错了！
        Integer age1 = null;
        Integer age2 = 0;

        System.out.println("-----------------");
        // 1、包装类可以把基本类型的数据转换成字符串形式。（没啥用）
        Integer i3 = 23;
        String rs = i3.toString();
        System.out.println(rs + 1);

        String rs1 = Integer.toString(i3);
        System.out.println(rs1 + 1);

        // 可以直接+字符串得到字符串类型
        String rs2 = i3 + "";
        System.out.println(rs2 + 1);

        System.out.println("-----------------");

        String number = "23";
        //转换成整数
        // int age = Integer.parseInt(number);
        int age = Integer.valueOf(number);
        System.out.println(age + 1);

        String number1 = "99.9";
        //转换成小数
//        double score = Double.parseDouble(number1);
        double score = Double.valueOf(number1);
        System.out.println(score + 0.1);
    }
}

四.正则表达式

• ①Data
• ②SimpleDataFormat
• ③Calendar
• ①概述LocalTime/LocalDate/LocalDateTime
• • 1.localDate
  • 2.localTime
  • 3.localDateTime
  • 4.updateTime
• ②instant
• ③DateTimeFormatter
• ④Duration/Period
• ⑤ChronoUnit