How do I compare two dates?

By I Wayan Saryada in Core API, Util Package 0 Comment

In this example you’ll see the utilization of SimpleDateFormat class for comparing two dates for equality. We convert the date object into string using the DateFormat instance and then compare it using String.equals() method.

package org.kodejava.util;

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

public class ComparingDate {
    public static void main(String[] args) {
        // Create a SimpleDateFormat instance with dd/MM/yyyy format
        DateFormat df = new SimpleDateFormat("dd/MM/yyyy");

        // Get the current date
        Date today = new Date();

        // Create an instance of calendar that represents a new year date
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DATE, 1);
        calendar.set(Calendar.MONTH, Calendar.JANUARY);
        calendar.set(Calendar.YEAR, 2021);

        String newYear = df.format(calendar.getTime());
        String now = df.format(today);

        // Using the string equals method we can compare the date.
        if (now.equals(newYear)) {
            System.out.println("Happy New Year!");
        } else {
            System.out.println("Have a nice day!");
        }
    }
}

How do I check if a string is a valid date?

By I Wayan Saryada in Core API, Text Package 1 Comment

The following code can be used to validate if a string contains a valid date information. The pattern of the date is defined by the java.text.SimpleDateFormat object. When the date is not valid a java.text.ParseException will be thrown.

package org.kodejava.text;

import java.text.SimpleDateFormat;
import java.text.ParseException;

public class DateValidation {
    public static void main(String[] args) {
        SimpleDateFormat format = new SimpleDateFormat("dd/MM/yyyy");

        // Input to be parsed should strictly follow the defined date format
        // above.
        format.setLenient(false);

        String date = "29/18/2021";
        try {
            format.parse(date);
        } catch (ParseException e) {
            System.out.println("Date " + date + " is not valid according to " +
                    format.toPattern() + " pattern.");
        }
    }
}

The result of the above date validation code is:

Date 29/18/2021 is not valid according to dd/MM/yyyy pattern.

How do I change date formatting symbols?

By I Wayan Saryada in Core API, Text Package 0 Comment

This example shows how we can change the date formatting symbols. In this example we change the month names and short month names and also the weekday names and short weekday names.

Other than these two items we can also change other symbols such as the Era name and AM-PM string.

package org.kodejava.text;

import java.text.SimpleDateFormat;
import java.text.DateFormat;
import java.text.DateFormatSymbols;
import java.util.Date;

public class DateFormatSymbolsExample {
    public static void main(String[] args) {
        // Defining a new Date Format Symbols, the following are month and day
        // names in Bahasa Indonesia.
        String[] newMonths = {"JANUARI", "FEBRUARI", "MARET", "APRIL", "MEI",
                "JUNI", "JULI", "AGUSTUS", "SEPTEMBER", "OKTOBER", "NOVEMBER",
                "DESEMBER"};
        String[] newShortMonths = {"JAN", "FEB", "MAR", "APR", "MEI", "JUN",
                "JUL", "AGU", "SEP", "OKT", "NOV", "DES"};
        String[] newWeekdays = {"", "MINGGU", "SENIN", "SELASA", "RABU", "KAMIS",
                "JUMAT", "SABTU"};
        String[] shortWeekdays = {"", "MIN", "SEN", "SEL", "RAB", "KAM", "JUM",
                "SAB"};

        DateFormatSymbols symbols = new DateFormatSymbols();
        symbols.setMonths(newMonths);
        symbols.setShortMonths(newShortMonths);
        symbols.setWeekdays(newWeekdays);
        symbols.setShortWeekdays(shortWeekdays);

        DateFormat format = new SimpleDateFormat("dd MMMM yyyy", symbols);
        System.out.println(format.format(new Date()));

        format = new SimpleDateFormat("dd MMM yyyy", symbols);
        System.out.println(format.format(new Date()));

        format = new SimpleDateFormat("EEEE, dd MMM yyyy", symbols);
        System.out.println(format.format(new Date()));

        format = new SimpleDateFormat("E, dd MMM yyyy", symbols);
        System.out.println(format.format(new Date()));
    }
}

The result of the code snippet above is:

02 OKTOBER 2021
02 OKT 2021
SABTU, 02 OKT 2021
SAB, 02 OKT 2021

How do I convert milliseconds value to date?

By I Wayan Saryada in Core API, Util Package 0 Comment 
package org.kodejava.util;

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

public class MillisecondsToDate {
    public static void main(String[] args) {
        // Create a DateFormatter object for displaying date information.
        DateFormat formatter = new SimpleDateFormat("dd/MM/yyyy hh:mm:ss.SSS");

        // Get date and time information in milliseconds
        long now = System.currentTimeMillis();

        // Create a calendar object that will convert the date and time value
        // in milliseconds to date. We use the setTimeInMillis() method of the
        // Calendar object.
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(now);

        System.out.println(now + " = " + formatter.format(calendar.getTime()));
    }
}

The output of the code snippet above is:

1632868662762 = 29/09/2021 06:37:42.762

How do I set default Locale?

By I Wayan Saryada in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.Random;

public class DefaultLocaleExample {
    public static void main(String[] args) {
        // Use Random class to generate some random number
        Random random = new Random();

        // We use the system default locale to format a number and a date.
        NumberFormat formatter = new DecimalFormat();
        Locale locale = Locale.getDefault();
        System.out.println("Default Locale = " + locale);
        System.out.println("Number         = " + formatter.format(random.nextDouble()));
        System.out.println("Date           = " + new SimpleDateFormat().format(new Date()));

        // We change the default locale to Locale.ITALY by setting it through 
        // the Locale.setDefault() method, and then we format another number
        // and date using a new locale. This change will affect all the class 
        // that aware to the Locale, such as the NumberFormat class.
        Locale.setDefault(Locale.ITALY);
        NumberFormat newFormatter = new DecimalFormat();
        System.out.println("New Locale     = " + Locale.getDefault());
        System.out.println("Number         = " + newFormatter.format(random.nextDouble()));
        System.out.println("Date           = " + new SimpleDateFormat().format(new Date()));
    }
}

The result of the code snippet above are:

Default Locale = en_US
Number         = 0.557
Date           = 9/26/21, 12:05 PM
New Locale     = it_IT
Number         = 0,217
Date           = 26/09/21, 12:05