如何查找多个年份而不只是一个年份的复活节日期？

Question

So far i have a code that calculates the date that Easter falls on once you input a year. I need to change it so that it gives you multiple dates for multiple years (you input 2 years instead and it gives everything in between). Hope that makes sense!

I'm not sure what i'm meant to do here. We've learnt forloops (note: we are just learning java) so I tried putting a forloop for the code but came up short because im not sure how that would work.

import java.util.Scanner;

public static void main(String[] args) {
    System.out.print("Please enter a year to calculate Easter Sunday\n>");
    Scanner sc = new Scanner(System.in);//imports java.util.Scanner to the library
    int aNumber = sc.nextInt();//saves next inputted number as "aNumber"

    while (aNumber <=0){//while statement to make sure inputted year is positive
        System.out.println("Please enter a postive year: ");
        aNumber = sc.nextInt();

    }

    int a = aNumber % 19,
        b = aNumber / 100,
        c = aNumber % 100,
        d = b / 4,
        e = b % 4,
        g = (8 * b + 13) / 25,
        h = (19 * a + b - d - g + 15) % 30,
        j = c / 4,
        k = c % 4,
        m = (a + 11 * h) / 319,
        r = (2 * e + 2 * j - k - h + m + 32) % 7,
        month = (h - m + r + 90) / 25, //determines month as a number
        date = (h - m + r + month + 19) % 32;//determines date

    String test;
    switch(month)//switch case to convert "month" to a string 
    {
        case 1:
            test = "January ";
            break;
        case 2:
            test = "February ";
            break;
        case 3:
            test = "March ";
            break;
        case 4:
            test = "April ";
            break;
        case 5:
            test = "May ";
            break;
        case 6:
            test = "June ";
            break;
        case 7:
            test = "July ";
            break;
        case 8:
            test = "August ";
            break;
        case 9:
            test = "September ";
            break;
        case 10:
            test = "October ";
            break;
        case 11:
            test = "November ";
            break;
        case 12:
            test = "December ";
            break;
        default:
            test = "error";
    }
    System.out.println("In " + aNumber + ", Easter Sunday will be on " + test + "" + date  + ".");//displays year,date and month of Easter Sunday
}

I meant to get multiple dates for every year between the two years you input.

Answer 1

Ok, provided that your code calculates Easter correctly, aim for something like this:

static String printEasterFor(int aNumber) {
        int a = aNumber % 19,
                b = aNumber / 100,
                c = aNumber % 100,
                d = b / 4,
                e = b % 4,
                g = (8 * b + 13) / 25,
                h = (19 * a + b - d - g + 15) % 30,
                j = c / 4,
                k = c % 4,
                m = (a + 11 * h) / 319,
                r = (2 * e + 2 * j - k - h + m + 32) % 7,
                month = (h - m + r + 90) / 25, //determines month as a number
                date = (h - m + r + month + 19) % 32;//determines date

        String test;
        switch(month)//switch case to convert "month" to a string
        {
            case 1:
                test = "January ";
                break;
            case 2:
                test = "February ";
                break;
            case 3:
                test = "March ";
                break;
            case 4:
                test = "April ";
                break;
            case 5:
                test = "May ";
                break;
            case 6:
                test = "June ";
                break;
            case 7:
                test = "July ";
                break;
            case 8:
                test = "August ";
                break;
            case 9:
                test = "September ";
                break;
            case 10:
                test = "October ";
                break;
            case 11:
                test = "November ";
                break;
            case 12:
                test = "December ";
                break;
            default:
                test = "error";
        }

        return "In " + aNumber + ", Easter Sunday will be on " + test + "" + date  + ".";//displays year,date and month of Easter Sunday
    }


    static List<String> showEasterBetween(int start, int end) {
        List<String> result = new ArrayList<>();
        IntStream.range(start, end).forEach(year -> result.add(printEasterFor(year)));

        return result;
    }

Then you call this like:

public static void main(String[] args) {
    int startYear = 2005;
    int endYear = 2025;
    List<String> easters = showEasterBetween(startYear, endYear);
}

As an improvement, your method printEasterFor could return a LocalDate object instead of printing a String, but I hope that you get my idea.

Answer 2

java.time

The Answer by mate00 seems correct. As mentioned there, you should be using the java.time types. Let's take the code shown in that other Answer, and make it more spiffy with the modern date-time classes. We also change some names for clarity.

We have a Year class. Using that Year type as the argument to your methods makes your code more self-documenting.

Year year = Year.of( 2019 ) ; 

We have LocalDate to represent a date-only value, without time-of-day and without time zone.

LocalDate localDate = LocalDate.of( 2019 , Month.JANUARY , 23 ) ;

And we have the Month enum, predefining an object for each month of a year. Using the Month enum, we can collapse your long switch statement to one or two lines. The Month.values() method generates an array of all the objects pre-instantiated by the enum. We can pick a month from that array by number. But we must use annoying zero-based index counting. Subtract one from 1-12 to get 0-11.

Month month = Month.values()[ 1-1 ];  // Get `Month.JANUARY` object for month number 1 (index number 0). 

Example code

Here is an entire example class, Easter with a pair of methods overloading of (passing either a single year or a pair of years). Perhaps forYear and forYears might be better method names, given the established java.time naming conventions . Ideal name would be for but that is a reserved keyword for the for loop.

Beware: I have not tested the results of this code. Use at your own risk.

package work.basil.example;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

import java.time.*;

public class Easter
{

    static LocalDate of ( Year year )
    {
        int yearNumber = year.getValue(); // Convert from object to simple integer.
        int a = yearNumber % 19,
                b = yearNumber / 100,
                c = yearNumber % 100,
                d = b / 4,
                e = b % 4,
                g = ( 8 * b + 13 ) / 25,
                h = ( 19 * a + b - d - g + 15 ) % 30,
                j = c / 4,
                k = c % 4,
                m = ( a + 11 * h ) / 319,
                r = ( 2 * e + 2 * j - k - h + m + 32 ) % 7,
                monthNumber = ( h - m + r + 90 ) / 25, //determines month as a number
                dayOfMonth = ( h - m + r + monthNumber + 19 ) % 32;//determines date

        int monthIndex = ( monthNumber - 1 ); // Convert from ordinal number to index number, zero-based for accessing an array in Java.
        Month month = Month.values()[ monthIndex ];  // Get the `Month` enum object for this month index. Throws an exception if the month index is out of range of 0-11.

        LocalDate easter = LocalDate.of( yearNumber , month , dayOfMonth );
        return easter;
    }

    static List < LocalDate > of ( Year start , Year stop )
    {
        Objects.requireNonNull( start );
        Objects.requireNonNull( stop );
        if ( stop.isBefore( start ) )  // Verify the stop year is not before the start year. Defensive programming. 
        {
            throw new IllegalArgumentException( "The stop year cannot be before the start year. Message # 296232f7-0c6e-49c2-a462-851aa0b30352." );
        }
        List < LocalDate > easters = new ArrayList <>();
        Year year = start;
        while ( year.isBefore( stop ) )
        {
            LocalDate easter = Easter.of( year );  // Determine the date of Easter for this particular year.
            easters.add( easter );
            // Prepare for next loop.
            year = year.plusYears( 1L );  // Increment to the next year in succession.
        }

        return easters;
    }

    public static void main ( String[] args )
    {
        List < LocalDate > easters = Easter.of( Year.of( 2005 ) , Year.of( 2010 ) );
        System.out.println( "easters.toString(): " + easters );
    }
}

When run.

easters.toString(): [2005-03-27, 2006-04-16, 2007-04-08, 2008-03-23, 2009-04-12]

We don't really need the Month enum in this particular routine. We could just pass the monthNumber integer to the factory method LocalDate::of .

LocalDate easter = LocalDate.of( yearNumber , monthNumber , dayOfMonth );

Strings

To generate strings representing these LocalDate objects' value, use the DateTimeFormatter class, especially its ofLocalizedDate method. Search Stack Overflow for more info, as this has been covered many many times already.

DateTimeFormatter f = DateTimeFormatter.ofLocalizedDate( FormatStyle.FULL ).withLocale( Locale.CANADA_FRENCH) ;  // Or `Locale.US` etc.
String output = localDate.format( f ) ;

dimanche 27 mars 2005