JAVA---日期小练习

方法:

• demo1,demo2日期转换

• demo3打印日历

• demo4可以自定义获取6个随机数字或字母（0~9,a~z,A~Z混合一起）

• demo5自定义字符串获取6个随机组成的字符串

• demo6求两个日期间隔

• demo7给某个日期加天数

 

package exercises;
​
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.Calendar;
import java.util.Date;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;
​
public class Exercise {
​
​
    public static void main(String[] args) {
​
​
        //String时间  与  日期对象相互转换
​
        // String dateStr = "2020-01-01 12:00:00";
//        System.out.println(demo1(dateStr));//Wed Jan 01 12:00:00 CST 2020
​
//        Date date = new Date();//当前计算机时间
//        System.out.println(demo2(date));
​
        // String 转  LocalDateTime
​
        // System.out.println(LocalDateTime.parse(dateStr, FORMATTER));//2020-01-01T12:00
​
//        LocalDateTime localDateTime = LocalDateTime.now();
//        System.out.println(localDateTime.format(FORMATTER));
​
        //demo7(new Date(), 5);
        demo3();
​
    }
​
    private static void demo7(Date date, int day) {
​
//        long time = date.getTime();
//        System.out.println(new Date(time + day * 24 * 3600 * 1000));
​
        //Calendar
        //date转Calendar
​
      /*  Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.add(Calendar.DATE,day);
​
        Date time = calendar.getTime();
        System.out.println(time);*/
​
​
        //LocalDate
//        System.out.println(LocalDate.of(2019, Month.OCTOBER, 10).plus(Period.ofDays(day)));
        System.out.println(LocalDate.of(2019, Month.OCTOBER, 10).plusDays(day));
    }
​
    private static void demo6() {
        LocalDateTime localDateTime1 = LocalDateTime.now();
        LocalDateTime localDateTime2 = LocalDateTime.of(2021, Month.MAY, 24, 12, 30, 30);
        //间隔  小时
        System.out.println(Math.abs(localDateTime1.until(localDateTime2, ChronoUnit.HOURS)));
​
​
    }
​
    private static void demo5() {
​
        String str = "小黑子鸡你太美!+daw234";
​
        Random random = new Random();
        StringBuilder builder = new StringBuilder();
        int length = str.length();
        for (int i = 0; i < 6; i++) {
            builder.append(str.charAt(random.nextInt(length)));
        }
        System.out.println(builder);
​
    }
​
    private static void demo4() {
​
        //可以自定义获取6个随机数字或字母（0~9,a~z,A~Z混合一起）
        // Random random = new Random();
​
        ThreadLocalRandom random = ThreadLocalRandom.current();
​
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < 6; i++) {
            int num = random.nextInt(48, 123);// 48-57  97-122  65-90
            if (num >= 48 && num <= 57) {//0-9
                builder.append(num - 48);
            } else if ((num >= 65 && num <= 90) || (num >= 97 && num <= 122)) {//A-Z  a-z
                builder.append((char) num);
            } else {
                i--;
            }
        }
        System.out.println(builder.toString());
    }
​
    private static void demo3() {
        //使用Calendar类的相关属性以及方法
        //1.获得Calendar类对象
        Calendar calendar = Calendar.getInstance();//获得当前系统默认时间
​
        //calendar.set(Calendar.MONTH, Calendar.FEBRUARY);
​
​
        calendar.set(Calendar.DAY_OF_MONTH, 1);
​
        int totalDays = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
​
        System.out.println("日\t1\t2\t3\t4\t5\t6");
        //当前月1号  属于这一周的第几天
        int num = calendar.get(Calendar.DAY_OF_WEEK);
​
        for (int i = 1; i < num; i++) {
            System.out.print("\t");
        }
​
        for (int i = 1; i <= totalDays; i++) {
            System.out.print(i + "\t");
            calendar.set(Calendar.DAY_OF_MONTH, i);
            int day = calendar.get(Calendar.DAY_OF_WEEK);
            if (day %7==0) {
                System.out.println();
            }
        }
    }
​
​
    private static final DateTimeFormatter FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
​
    // private static final DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    //ThreadLocal
​
    private static final ThreadLocal<DateFormat> LOCAL = new ThreadLocal() {
        @Override
        protected SimpleDateFormat initialValue() {
            return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        }
    };
​
    private static String demo2(Date date) {
        return LOCAL.get().format(date);
    }
​
    private static Date demo1(String dateStr) {
​
        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        //SimpleDateFormat dateFormat = new SimpleDateFormat();
        try {
            Date date = LOCAL.get().parse(dateStr);
            return date;
        } catch (ParseException e) {
            e.printStackTrace();
        }
​
        return null;
    }
​
}