java - 关于带有日期和随机数的程序的问题

Question

我正在尝试创建一个生成随机数的程序。当生成的随机数与当前日期匹配时，它会打印一个计数器来记录它尝试了多少次。日期格式为 ddMMyyyy，生成的随机数为 8 位。最后，它会打印五次日期和计数。这是我到目前为止所拥有的，但它永远不会返回输出。

import java.util.Random;
import java.util.Date;
import java.text.*;

public class Program1 {

    public static void main(String[] args) {

        Date date = new Date();
        Random value = new Random();
        int x = value.nextInt();

        int counter = 0;

        do {
            counter++;
        } while(!date.equals(value));

        if (date.equals(value)){
            for(int i = 1; i < 6; i++) {
                SimpleDateFormat sdf = new SimpleDateFormat ("ddMMyyyy");
                System.out.println("The date is " + sdf.format(date) + "!");
                System.out.println("The Count is: " + counter);
                System.out.println();
            }
        }
    }
}

标签： javadaterandomcounterjava-time

Answer 1

获取long0 到从纪元开始的毫秒数范围内的数字，并应用格式化程序以获取所需格式的日期字符串。然后将其与今天的日期字符串进行比较。

演示：

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Objects;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;

class Main {
    public static void main(String[] args) {
        Date now = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("ddMMyyyy");
        String strToday = sdf.format(now);
        int counter = 0;

        while (true) {
            // Instantiate Date with minutes of 8 digits
            Date date = new Date(TimeUnit.MILLISECONDS
                    .convert(ThreadLocalRandom.current().nextLong(10000000, 100000000), TimeUnit.MINUTES));
            String strDate = sdf.format(date);
            if (Objects.equals(strToday, strDate)) {
                for (int i = 1; i < 6; i++) {
                    System.out.println("The date is " + strDate + "!");
                    System.out.println("The Count is: " + counter);
                    System.out.println();
                }
                break;
            } else {
                counter++;
            }
        }
    }
}

示例运行：

The date is 21032021!
The Count is: 33263

The date is 21032021!
The Count is: 33263

The date is 21032021!
The Count is: 33263

The date is 21032021!
The Count is: 33263

The date is 21032021!
The Count is: 33263

请注意，java.util日期时间 API 及其格式化 APISimpleDateFormat已过时且容易出错。建议完全停止使用它们并切换到现代日期时间 API。^*

使用现代日期时间 API：

import java.time.Instant;
import java.time.LocalDate;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;
import java.util.Objects;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;

class Main {
    public static void main(String[] args) {
        // Change the ZoneId as applicable e.g. ZoneId.of("Europe/London")
        ZoneId zoneId = ZoneId.systemDefault();

        ZonedDateTime now = ZonedDateTime.now(zoneId);
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("ddMMuuuu", Locale.ENGLISH);
        String strToday = dtf.format(now);
        int counter = 0;

        while (true) {
            // Instantiate Date with minutes of 8 digits
            LocalDate date = Instant
                    .ofEpochMilli(TimeUnit.MILLISECONDS
                            .convert(ThreadLocalRandom.current().nextLong(10000000, 100000000), TimeUnit.MINUTES))
                    .atZone(zoneId).toLocalDate();
            String strDate = dtf.format(date);
            if (Objects.equals(strToday, strDate)) {
                for (int i = 1; i < 6; i++) {
                    System.out.println("The date is " + strDate + "!");
                    System.out.println("The Count is: " + counter);
                    System.out.println();
                }
                break;
            } else {
                counter++;
            }
        }
    }
}

示例运行：

The date is 21032021!
The Count is: 9097

The date is 21032021!
The Count is: 9097

The date is 21032021!
The Count is: 9097

The date is 21032021!
The Count is: 9097

The date is 21032021!
The Count is: 9097

---

^{* 出于任何原因，如果您必须坚持使用 Java 6 或 Java 7，则可以使用ThreeTen-Backport，它将大部分java.time功能向后移植到 Java 6 和 7。如果您正在为 Android 项目和 Android API 工作level 仍然不符合 Java-8，请检查Java 8+ APIs available through desugaring和How to use ThreeTenABP in Android Project。}