如何解决打印给定年份的所有周五和周六的问题？

Question

我正试着打印任何一年的所有星期六和星期日。但出于某种原因，该程序不会只打印星期六，也不会打印2022年的星期五。一年来，我尝试过不同的价值观，但除了2022年之外，我仍然没有找到任何价值。我在这里做错了什么？贝娄是密码。

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Scanner;

public class JavaDayFinder extends Thread {

    int day;
    int year;

    JavaDayFinder(int day, int year) {
        this.day = day;
        this.year = year;
    }

    @Override
    public void run() {
        Calendar calendar = new GregorianCalendar();
        calendar.set(year, Calendar.JANUARY, 1);
        calendar.getTime();
        calendar.set(Calendar.DAY_OF_WEEK, day);
        calendar.getTime();

        while (calendar.get(Calendar.YEAR) == year) {
            System.out.println(calendar.getTime());
            calendar.add(Calendar.DAY_OF_MONTH, 7);
            try {
                Thread.sleep(250);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }

    public static void main(String[] args) {
        System.out.println("This program prints all the common holidays (Fridays & Saturdays) of any given year.");
        System.out.print("Please input the year of which you want to know the holidays: ");
        Scanner scan = new Scanner(System.in);
        int year = scan.nextInt();
        System.out.println("Given year : " + year);
        System.out.println();

        JavaDayFinder friday = new JavaDayFinder(6, year);
        JavaDayFinder saturday = new JavaDayFinder(7, year);
        friday.start();
        saturday.start();
    }
}

波纹管是输出

This program prints all the common holidays (Fridays & Saturdays) of any given year.
Please input the year of which you want to know the holidays: 2022
Given year : 2022

Sat Jan 01 17:05:56 BDT 2022
Sat Jan 08 17:05:56 BDT 2022
Sat Jan 15 17:05:56 BDT 2022
Sat Jan 22 17:05:56 BDT 2022
Sat Jan 29 17:05:56 BDT 2022
Sat Feb 05 17:05:56 BDT 2022
Sat Feb 12 17:05:56 BDT 2022
Sat Feb 19 17:05:56 BDT 2022
Sat Feb 26 17:05:56 BDT 2022
Sat Mar 05 17:05:56 BDT 2022
Sat Mar 12 17:05:56 BDT 2022
Sat Mar 19 17:05:56 BDT 2022
Sat Mar 26 17:05:56 BDT 2022
Sat Apr 02 17:05:56 BDT 2022
Sat Apr 09 17:05:56 BDT 2022
Sat Apr 16 17:05:56 BDT 2022
Sat Apr 23 17:05:56 BDT 2022
Sat Apr 30 17:05:56 BDT 2022
Sat May 07 17:05:56 BDT 2022
Sat May 14 17:05:56 BDT 2022
Sat May 21 17:05:56 BDT 2022
Sat May 28 17:05:56 BDT 2022
Sat Jun 04 17:05:56 BDT 2022
Sat Jun 11 17:05:56 BDT 2022
Sat Jun 18 17:05:56 BDT 2022
Sat Jun 25 17:05:56 BDT 2022
Sat Jul 02 17:05:56 BDT 2022
Sat Jul 09 17:05:56 BDT 2022
Sat Jul 16 17:05:56 BDT 2022
Sat Jul 23 17:05:56 BDT 2022
Sat Jul 30 17:05:56 BDT 2022
Sat Aug 06 17:05:56 BDT 2022
Sat Aug 13 17:05:56 BDT 2022
Sat Aug 20 17:05:56 BDT 2022
Sat Aug 27 17:05:56 BDT 2022
Sat Sep 03 17:05:56 BDT 2022
Sat Sep 10 17:05:56 BDT 2022
Sat Sep 17 17:05:56 BDT 2022
Sat Sep 24 17:05:56 BDT 2022
Sat Oct 01 17:05:56 BDT 2022
Sat Oct 08 17:05:56 BDT 2022
Sat Oct 15 17:05:56 BDT 2022
Sat Oct 22 17:05:56 BDT 2022
Sat Oct 29 17:05:56 BDT 2022
Sat Nov 05 17:05:56 BDT 2022
Sat Nov 12 17:05:56 BDT 2022
Sat Nov 19 17:05:56 BDT 2022
Sat Nov 26 17:05:56 BDT 2022
Sat Dec 03 17:05:56 BDT 2022
Sat Dec 10 17:05:56 BDT 2022
Sat Dec 17 17:05:56 BDT 2022
Sat Dec 24 17:05:56 BDT 2022
Sat Dec 31 17:05:56 BDT 2022

Process finished with exit code 0

Answer 1

tl;dr

使用java.time类、流、lambdas和谓词摘录代码。

this.datesOfYearforDaysOfWeek(
        Year.of( 2023 ) ,
        Set.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY )
)

year.atDay( 1 )
        .datesUntil(
                year
                        .plusYears( 1 )
                        .atDay( 1 )
        )
        .filter(
                date -> dows.contains( date.getDayOfWeek() )
        )
        .toList()

详细信息

MC皇帝的回答是正确的和明智的。为了好玩，我将展示一种不同的方法。虽然我还没有测试性能，但可能没有那么有效率。在这里我们使用溪流和兰巴达。

我们使用LocalDate#datesUntil来获取一个LocalDate对象流。注意，datesUntil方法使用半开放逻辑，其中开头是包含的，而结尾是独占的。因此，一年从第一年开始，一直持续到第一年，但不包括第一年。

Year类代表了一年的时间，使代码更加清晰和自文档化。

主要逻辑：

    LocalDate firstOfYear = year.atDay( 1 );
    List < LocalDate > dates =
            firstOfYear
                    .datesUntil( firstOfYear.plusYears( 1 ) )
                    .filter(
                            date -> dows.contains( date.getDayOfWeek() )
                    )
                    .toList();

完整的方法。

List < LocalDate > datesOfYearforDaysOfWeek ( final Year year , final Set < DayOfWeek > dows )
{
    // Validate inputs.
    Objects.requireNonNull( year );
    Objects.requireNonNull( dows );
    if ( dows.isEmpty() ) { throw new IllegalArgumentException( "Days of week is empty." ); }

    // Logic
    LocalDate firstOfYear = year.atDay( 1 );
    List < LocalDate > dates =
            firstOfYear
                    .datesUntil( firstOfYear.plusYears( 1 ) )
                    .filter(
                            date -> dows.contains( date.getDayOfWeek() )
                    )
                    .toList();

    // Result.
    return List.copyOf( dates );  // Effectively a no-op if already an immutable list.
}

使用。

List < LocalDate > dates =
        this.datesOfYearforDaysOfWeek(
                Year.of( 2023 ) ,
                Set.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY )
        );

跑的时候。

dates.toString() = [2023-01-01, 2023-01-07, 2023-01-08, 2023-01-14, 2023-01-15, 2023-01-21, 2023-01-22, 2023-01-28, 2023-01-29, 2023-02-04, 2023-02-05, 2023-02-11, 2023-02-12, 2023-02-18, 2023-02-19, 2023-02-25, 2023-02-26, 2023-03-04, 2023-03-05, 2023-03-11, 2023-03-12, 2023-03-18, 2023-03-19, 2023-03-25, 2023-03-26, 2023-04-01, 2023-04-02, 2023-04-08, 2023-04-09, 2023-04-15, 2023-04-16, 2023-04-22, 2023-04-23, 2023-04-29, 2023-04-30, 2023-05-06, 2023-05-07, 2023-05-13, 2023-05-14, 2023-05-20, 2023-05-21, 2023-05-27, 2023-05-28, 2023-06-03, 2023-06-04, 2023-06-10, 2023-06-11, 2023-06-17, 2023-06-18, 2023-06-24, 2023-06-25, 2023-07-01, 2023-07-02, 2023-07-08, 2023-07-09, 2023-07-15, 2023-07-16, 2023-07-22, 2023-07-23, 2023-07-29, 2023-07-30, 2023-08-05, 2023-08-06, 2023-08-12, 2023-08-13, 2023-08-19, 2023-08-20, 2023-08-26, 2023-08-27, 2023-09-02, 2023-09-03, 2023-09-09, 2023-09-10, 2023-09-16, 2023-09-17, 2023-09-23, 2023-09-24, 2023-09-30, 2023-10-01, 2023-10-07, 2023-10-08, 2023-10-14, 2023-10-15, 2023-10-21, 2023-10-22, 2023-10-28, 2023-10-29, 2023-11-04, 2023-11-05, 2023-11-11, 2023-11-12, 2023-11-18, 2023-11-19, 2023-11-25, 2023-11-26, 2023-12-02, 2023-12-03, 2023-12-09, 2023-12-10, 2023-12-16, 2023-12-17, 2023-12-23, 2023-12-24, 2023-12-30, 2023-12-31]

使更紧凑，虽然不一定更好。同样的结果。

    // Logic
    List < LocalDate > dates =
            year.atDay( 1 )
                    .datesUntil(
                            year
                                    .plusYears( 1 )
                                    .atDay( 1 )
                    )
                    .filter(
                            date -> dows.contains( date.getDayOfWeek() )
                    )
                    .toList();

遗嘱执行人服务

您可能希望使用遗嘱执行人服务而不是自己管理线程。

将任务定义为返回所需日期列表的Callable。用所需的年份和星期数来构造对象.

class DatesForDayOfWeekTask implements Callable < List < LocalDate > >
{
    Year year;
    DayOfWeek dow;

    public DatesForDayOfWeekTask ( final Year year , final DayOfWeek dow )
    {
        this.year = year;
        this.dow = dow;
    }

    @Override
    public List < LocalDate > call ( ) throws Exception
    {
        return datesOfYearforDaysOfWeek( this.year , Set.of( this.dow ) );
    }
}

示例用法。

System.out.println( "INFO - Demo started. " + Instant.now() );

ExecutorService executorService = Executors.newCachedThreadPool();

DatesForDayOfWeekTask saturdayTask = new DatesForDayOfWeekTask( Year.of( 2023 ) , DayOfWeek.SATURDAY );
DatesForDayOfWeekTask sundayTask = new DatesForDayOfWeekTask( Year.of( 2023 ) , DayOfWeek.SUNDAY );

Future < List < LocalDate > > saturdayFuture = executorService.submit( saturdayTask );
Future < List < LocalDate > > sundayFuture = executorService.submit( sundayTask );

System.out.println( "INFO Tasks submitted. Please wait. " + Instant.now() );
try { Thread.sleep( Duration.ofSeconds( 10 ).toMillis() ); } catch ( InterruptedException e ) { throw new RuntimeException( e ); }
this.shutdownAndAwaitTermination( executorService );

try
{
    System.out.println( "saturdayFuture.get() = " + saturdayFuture.get() );
    System.out.println( "sundayFuture.get() = " + sundayFuture.get() );
}
catch ( InterruptedException e ) { throw new RuntimeException( e ); }
catch ( ExecutionException e ) { throw new RuntimeException( e ); }
System.out.println( "INFO - Demo ended. " + Instant.now() );

跑的时候。

INFO - Demo started. 2022-09-28T00:38:58.460930Z
INFO Tasks submitted. Please wait. 2022-09-28T00:38:58.469034Z
saturdayFuture.get() = [2023-01-07, 2023-01-14, 2023-01-21, 2023-01-28, 2023-02-04, 2023-02-11, 2023-02-18, 2023-02-25, 2023-03-04, 2023-03-11, 2023-03-18, 2023-03-25, 2023-04-01, 2023-04-08, 2023-04-15, 2023-04-22, 2023-04-29, 2023-05-06, 2023-05-13, 2023-05-20, 2023-05-27, 2023-06-03, 2023-06-10, 2023-06-17, 2023-06-24, 2023-07-01, 2023-07-08, 2023-07-15, 2023-07-22, 2023-07-29, 2023-08-05, 2023-08-12, 2023-08-19, 2023-08-26, 2023-09-02, 2023-09-09, 2023-09-16, 2023-09-23, 2023-09-30, 2023-10-07, 2023-10-14, 2023-10-21, 2023-10-28, 2023-11-04, 2023-11-11, 2023-11-18, 2023-11-25, 2023-12-02, 2023-12-09, 2023-12-16, 2023-12-23, 2023-12-30]
sundayFuture.get() = [2023-01-01, 2023-01-08, 2023-01-15, 2023-01-22, 2023-01-29, 2023-02-05, 2023-02-12, 2023-02-19, 2023-02-26, 2023-03-05, 2023-03-12, 2023-03-19, 2023-03-26, 2023-04-02, 2023-04-09, 2023-04-16, 2023-04-23, 2023-04-30, 2023-05-07, 2023-05-14, 2023-05-21, 2023-05-28, 2023-06-04, 2023-06-11, 2023-06-18, 2023-06-25, 2023-07-02, 2023-07-09, 2023-07-16, 2023-07-23, 2023-07-30, 2023-08-06, 2023-08-13, 2023-08-20, 2023-08-27, 2023-09-03, 2023-09-10, 2023-09-17, 2023-09-24, 2023-10-01, 2023-10-08, 2023-10-15, 2023-10-22, 2023-10-29, 2023-11-05, 2023-11-12, 2023-11-19, 2023-11-26, 2023-12-03, 2023-12-10, 2023-12-17, 2023-12-24, 2023-12-31]
INFO - Demo ended. 2022-09-28T00:39:08.480522Z

完整的示例代码。

package work.basil.example.days;

import java.time.*;
import java.util.List;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.*;

public class App
{
    public static void main ( String[] args )
    {
        App app = new App();
//        app.demo();
        app.demoThreaded();
    }

    private void demo ( )
    {
        List < LocalDate > dates =
                this.datesOfYearforDaysOfWeek(
                        Year.of( 2023 ) ,
                        Set.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY )
                );
        System.out.println( "dates.toString() = " + dates );
    }

    List < LocalDate > datesOfYearforDaysOfWeek ( final Year year , final Set < DayOfWeek > dows )
    {
        // Validate inputs.
        Objects.requireNonNull( year );
        Objects.requireNonNull( dows );
        if ( dows.isEmpty() ) { throw new IllegalArgumentException( "Days of week is empty." ); }

        // Logic
        List < LocalDate > dates =
                year.atDay( 1 )
                        .datesUntil(
                                year
                                        .plusYears( 1 )
                                        .atDay( 1 )
                        )
                        .filter(
                                date -> dows.contains( date.getDayOfWeek() )
                        )
                        .toList();

        // Result.
        return List.copyOf( dates );  // Effectively a no-op if already an immutable list.
    }

    private void demoThreaded ( )
    {
        System.out.println( "INFO - Demo started. " + Instant.now() );

        ExecutorService executorService = Executors.newCachedThreadPool();

        DatesForDayOfWeekTask saturdayTask = new DatesForDayOfWeekTask( Year.of( 2023 ) , DayOfWeek.SATURDAY );
        DatesForDayOfWeekTask sundayTask = new DatesForDayOfWeekTask( Year.of( 2023 ) , DayOfWeek.SUNDAY );

        Future < List < LocalDate > > saturdayFuture = executorService.submit( saturdayTask );
        Future < List < LocalDate > > sundayFuture = executorService.submit( sundayTask );

        System.out.println( "INFO Tasks submitted. Please wait. " + Instant.now() );
        try { Thread.sleep( Duration.ofSeconds( 10 ).toMillis() ); } catch ( InterruptedException e ) { throw new RuntimeException( e ); }
        this.shutdownAndAwaitTermination( executorService );

        try
        {
            System.out.println( "saturdayFuture.get() = " + saturdayFuture.get() );
            System.out.println( "sundayFuture.get() = " + sundayFuture.get() );
        }
        catch ( InterruptedException e ) { throw new RuntimeException( e ); }
        catch ( ExecutionException e ) { throw new RuntimeException( e ); }
        System.out.println( "INFO - Demo ended. " + Instant.now() );
    }


    class DatesForDayOfWeekTask implements Callable < List < LocalDate > >
    {
        Year year;
        DayOfWeek dow;

        public DatesForDayOfWeekTask ( final Year year , final DayOfWeek dow )
        {
            this.year = year;
            this.dow = dow;
        }

        @Override
        public List < LocalDate > call ( ) throws Exception
        {
            return datesOfYearforDaysOfWeek( this.year , Set.of( this.dow ) );
        }
    }


    // Boilerplate code taken from `ExecutorService` interface Javadoc, and slightly modified.
    private void shutdownAndAwaitTermination ( ExecutorService executorService )
    {
        executorService.shutdown(); // Disable new tasks from being submitted
        try
        {
            // Wait a while for existing tasks to terminate
            if ( ! executorService.awaitTermination( 60 , TimeUnit.SECONDS ) )
            {
                executorService.shutdownNow(); // Cancel currently executing tasks
                // Wait a while for tasks to respond to being cancelled
                if ( ! executorService.awaitTermination( 60 , TimeUnit.SECONDS ) )
                { System.err.println( "Pool did not terminate" ); }
            }
        }
        catch ( InterruptedException ex )
        {
            // (Re-)Cancel if current thread also interrupted
            executorService.shutdownNow();
            // Preserve interrupt status
            Thread.currentThread().interrupt();
        }
    }
}

Answer 2

解释：

如果1月1日是星期六，这意味着周的星期五将是1月1日的前1天，也就是12月31日，当您将下面的字段设置为星期五时，它将值设置为12月31日，并且由于您的时间条件，它不会执行循环。

calendar.set(Calendar.DAY_OF_WEEK, day);

这段代码不适用于边缘情况，也就是说，从星期六开始的任何一年都不会在周五打印。例如2011年、2028年等

以下方法设定为每月的第一个星期五/星期六/任何工作日：

    private void setNextAvailableDay(Calendar calendar, int day) {
        Date currTime = calendar.getTime();
        calendar.set(Calendar.DAY_OF_WEEK, day);
        if(currTime.after(calendar.getTime()))
            calendar.add(Calendar.DAY_OF_MONTH, 7);
    }

calendar.set(Calendar.DAY_OF_WEEK, day);
// can be replaced by
setNextAvailableDay(calendar, day)