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Anonymous Coward
Asked: 2020-01-02 01:14:55 +0800 CST 2020-01-02 01:14:55 +0800 CST

How do I check the validity of a date?

  • 772

I need to check that a date entered in a form is valid.

I have the date separated into year, day and month. And I'm not interested in checking dates before 1900.

I am doing it with this code: 

public class Fecha
{
    int año;
    int mes; // 1 a 12
    int dia; // 1 a 31
}

static int[] diasMes= {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
/**
 *   Comprueba si la fecha es correcta. Se comprueban solo fechas de 1900 
 * o posteriores.
 * @param fecha La fecha a comprobar.
 * @return true si la fecha es correcta, false en otro caso.
 * @throws IllegalArgumentException si el año es menor que 1900.
 */
boolean validaFecha( Fecha fecha)
{
    if ( fecha.año < 1900 ) {
        throw new IllegalArgumentException( 
                "Solo se comprueban fechas del año 1900 o posterior");
    }
    if ( fecha.mes<1 || fecha.mes>12 )
        return false;
    // Para febrero y bisiesto el limite es 29
    if ( fecha.mes==2 && fecha.año%4==0 )
        return fecha.dia>=1 && fecha.dia<=29;
    return fecha.dia>=0 && fecha.dia<=diasMes[fecha.mes-1];
}

The class FechaI use is somewhat more complicated, it has its setter, getter and other things, but those details are irrelevant to this question. The question is about the method validaFecha.

Is the implementation correct? Is there a way to do it with the standard libraries?

java

2 Answers

  1. Best Answer

    Is there a way to do it with the standard libraries?

    Depending on the version of Java you are using, you have access to some classes that are already included in the JDK without requiring an external library (additional JAR files).

    • Since Java 8

      If you're using Java 8, you can use class 1 to construct a date with the year, month, and day. Namely:java.time.LocalDate

      import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class Main {
    public static void main(String[] args) {
        int year = 2016;                   // año
        int month = 1;                     // mes [1,...,12]
        int dayOfMonth = 1;                // día [1,...,31]

        if (year < 1900) {
            throw new IllegalArgumentException("Año inválido.");
        } 

        LocalDate today = LocalDate.of(year, month, dayOfMonth);
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
        System.out.println(formatter.format(today)); // 01/01/2016
    }
}

      If any of the values ​​(year, month, day) are invalid, the method LocalDate.ofwill throw java.time.DateTimeException.

    • From JDK1.1

      java.util.DateIf you are using Java 6/7, you can use the and 2 classes to construct a date with the year, month, and day. Namely:java.util.Calendar

      import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class Main {
    public static void main(String[] args) {
        int year = 2016;                   // año
        int month = 1;                     // mes [1,...,12]
        int dayOfMonth = 1;                // día [1,...,31]

        if (year < 1900) {
            throw new IllegalArgumentException("Año inválido.");
        }

        Calendar calendar = Calendar.getInstance();
        calendar.setLenient(false);
        calendar.set(Calendar.YEAR, year);
        calendar.set(Calendar.MONTH, month - 1); // [0,...,11]
        calendar.set(Calendar.DAY_OF_MONTH, dayOfMonth);
        Date date = calendar.getTime();
        SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
        System.out.println(sdf.format(date)); // 01/01/2016
    }
}

      It must be specified calendar.setLenient(false);to only allow values ​​within the corresponding ranges (year, month, day). If any of these values ​​are invalid, it Calendarwill throw java.lang.IllegalArgumentException.

    ────────────
    1. You can see some examples of this and other classes in Java SE 8 Date and Time .
    2. You can see some examples in Java Date and Calendar examples . Also in Java Calendar Class .

    • 15

  2. Is the implementation correct?

    No. Based on your code, I would change this part:

    if (fecha.mes==2 && fecha.año%4==0)

    Since the rule for leap years is (emphasis mine):

    A year is a leap year if it is divisible by 4, unless it is divisible by 100 . However, if a year is divisible by 100 and is also divisible by 400, it is also a leap year . Obviously, this eliminates the end-of-century years (last of each century, which must end in 00) whose century is not a multiple of 4.

    This means:

    • If the year is a multiple of 400, it is a leap year.
    • Otherwise, if the year is a multiple of 4 and not 100, it is a leap year.

    The easiest way to adapt this in your code is:

    if (fecha.mes==2 && dia==29) {
        return fecha.año % 400 == 0 ||
               (fecha.año % 4 == 0 && fecha.año % 100 != 0);
}

    Another error you have is in this part:

    return fecha.dia >= 0 ...

    Which is on the last line of the method. Should befecha.dia >=1

    Is there a way to do it with the standard libraries?

    If you want to use the JDK classes, in addition to the options indicated by @PaulVargas, you can use SimpleDateFormat, available in any version of Java (since 1.5 that I remember). Here the code:

    boolean validaFecha( Fecha fecha) {
    if ( fecha.año < 1900 ) {
    throw new IllegalArgumentException( 
        "Solo se comprueban fechas del año 1900 o posterior");
    }
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    String fechaAValidar = String.format("%d-%d-%d", fecha.año, fecha.mes, fecha.dia);
    boolean result = true;
    try {
        sdf.parse(fechaAValidar);
    } catch (ParseException e) {
        //la excepción es silenciosa
        result = false;
    }
    return result;
}
    • 5