（1）

/**
 * @author: sunshine
 * @description:
 * @data: 2022/2/28  20:56
 * @version: 0.1
 * @since: jdk11
 */
//1.将长时间格式时间转换为字符串 yyyy-MM-dd HH:mm:ss
public class Exercise1 {
    public static void main(String[] args) {
     demo1();  //(jdk1.8之前)
     demo2();  //(jdk1.8之后)
    }

    private static void demo2() {
        LocalDateTime localDateTime = LocalDateTime.of(2022,Calendar.FEBRUARY,1,12,0,0);

        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(PATTERN);
        String format = formatter.format(localDateTime);
        System.out.println(format);

        //String format1 = localDateTime.format(formatter);

    }

    private static final String PATTERN = "yyyy-MM-dd HH:mm:ss";

    private static void demo1() {
       //Date转String
        //1.创建Date对象
        Date date = new Date();  //获得系统当前时间
        long time = date.getTime();  //获得毫秒数（不推荐）

        long millis = System.currentTimeMillis();  //推荐

        //创建Calender对象
        Calendar calendar = Calendar.getInstance();
        calendar.set(2022,Calendar.FEBRUARY,1,12,0,0);  //2022-2-1 12:00:00

        //Calender转Date
        Date date1 = calendar.getTime();

        //2.创建格式类DateFormat
        DateFormat dateFormat = new SimpleDateFormat(PATTERN);
        String dateStr = dateFormat.format(date);
        System.out.println(dateStr);
    }
}

（2）

/**
 * @author: sunshine
 * @description:
 * @data: 2022/2/28  21:22
 * @version: 0.1
 * @since: jdk11
 */
//2.使用Calendar类的相关属性以及方法！打印出某年某个月的日历信息！（要求年月日由命令行输入）
public class Exercise2 {
    public static void main(String[] args) {
        //demo3();
        demo4();
    }

    private static void demo4() {
        //动态月份的情况
        int year = 2022;
        Scanner input = new Scanner(System.in);
        System.out.println("请录入月份:");
        int month = input.nextInt();

        Calendar calendar = Calendar.getInstance();
        calendar.set(year,month-1,1);

        System.out.println("日\t一\t二\t三\t四\t五\t六");
        int totalDay = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);

        //判断1号有几个空格
        int day = calendar.get(Calendar.DAY_OF_WEEK);
        for (int i = 1; i < day; i++) {
            System.out.print("\t");
        }

        for (int i = 1; i <= totalDay; i++) {
            System.out.print(i+"\t");
            //判断当前天是否为一周最后一天，是则换行
            calendar.set(Calendar.DAY_OF_MONTH,i);
            if (calendar.get(Calendar.DAY_OF_WEEK)==7){
                System.out.println();
            }
        }

    }

    private static void demo3() {
        //固定月份的情况
        int year = 2022;
        int month = 2;

        Calendar calendar = Calendar.getInstance();
        calendar.set(year,month-1,1);     //2月份的序号是1

        System.out.println("日\t一\t二\t三\t四\t五\t六");
        int totalDay = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);

        System.out.print("\t\t");
        for (int i = 1; i <= totalDay; i++) {
            System.out.print(i+"\t");
            //判断当前天是否为一周最后一天，是则换行
            calendar.set(Calendar.DAY_OF_MONTH,i);
            if (calendar.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY){
                System.out.println();
            }
        }

    }
}

（3）

//4.计算两个时间相差几个小时
public class Exercise4 {
    public static void main(String[] args) {
        //demo1();
        demo2();
    }

    private static void demo2() {
        //LocalDateTime 与 LocalDateTime
        LocalDateTime dateTime1 = LocalDateTime.of(2022,Calendar.FEBRUARY,1,12,0,0);
        LocalDateTime dateTime2 = LocalDateTime.now();

        long hours = dateTime1.until(dateTime2, ChronoUnit.HOURS);  //括号里的减括号外面的
        System.out.println(hours);
    }

    private static void demo1() {
        //Date 与 Date
        Calendar calendar = Calendar.getInstance();
        calendar.set(2022,Calendar.FEBRUARY,1,12,0,0);  //2022-2-1 12:00:00
        Date date1 = calendar.getTime();
        Date date2 = new Date();

        long result = Math.abs((date1.getTime()-date2.getTime())/1000/3600);
        System.out.println(result);
    }
}

（4）

/**
 * @author: sunshine
 * @description:
 * @data: 2022/2/28  21:24
 * @version: 0.1
 * @since: jdk11
 */
//5.一个方法，要求传入时间和间隔天数，返回新的日期
public class Exercise5 {
    public static void main(String[] args) {
        demo1(new Date(),10);   //Date之间的操作
        demo2(LocalDate.now(),10);   //LocalDate之间的操作
    }

    private static LocalDate demo2(LocalDate localDate,int days) {
        return localDate.plusDays(days);

    }

    private static Date demo1(Date date,int days) {
         //传入时间加时间间隔
         //用毫秒数来写
        long time = date.getTime() + Duration.ofDays(days).toMillis();   //加号后面的是天转毫秒

        return new Date(time);
    }
}

（5）

/**
 * @author: sunshine
 * @description:
 * @data: 2022/2/28  21:24
 * @version: 0.1
 * @since: jdk11
 */
//6.要求写一个工具类，可以自定义获取N个随机数字或字母（0~9,a~z,A~Z混合一起）
public class Exercise6 {
    public static void main(String[] args) {
        demo1();
        //demo2();
    }

    private static void demo2() {
        StringBuilder builder = new StringBuilder();

        ThreadLocalRandom random = ThreadLocalRandom.current();
        int choice = random.nextInt(0,3);
        for (int i = 1; i <= 5; i++) {
            char ch = ' ';
            switch (choice) {
                case 0:
                    ch = (char)random.nextInt(48,57);
                    break;
                case 1:
                    ch = (char)random.nextInt(68,90);
                    break;
                case 2:
                    ch = (char)random.nextInt(97,122);
                    break;
            }
            builder.append(ch);
        }
        System.out.println(builder.toString());
    }

    private static void demo1() {
        //48-57 0-9      A-Z 65-90     a-z 97-122
        ThreadLocalRandom random = ThreadLocalRandom.current();

        StringBuilder builder = new StringBuilder();
        int count = 5;
        for(int i=1;i<=count;i++){
            int num = random.nextInt(48,122);
            if(num>=48 && num<=57){
                num = num -48;     //直接变成对应数字
                builder.append(num);
            }else if( (num>=65 && num<=90) || (num>=97 && num<=122) ){
                char ch = (char)num;    //数字转字符
                builder.append(ch);
            }else {
                i--;
            }
        }
        System.out.println(builder.toString());
    }
}