How do I read and write data in Windows registry?

By Wayan in Core API, Util Package 0 Comment

The java.util.prefs package provides a way for applications to store and retrieve user and system preferences and data configuration. These preference data will be stored persistently in an implementation-dependent backing stored. For example in Windows operating system in will stored in Windows registry.

To write and read these data we use the java.util.prefs.Preferences class. The following example will show you how to read and write to the HKCU (HKEY_CURRENT_USER) in the registry.

package org.kodejava.util.prefs;

import java.util.prefs.Preferences;

public class RegistryDemo {
    public static final String PREF_KEY = "kodejava";
    public static void main(String[] args) {
        // Write Preferences information to HKCU (HKEY_CURRENT_USER),
        // HKCU\SOFTWARE\JavaSoft\Prefs
        Preferences userPref = Preferences.userRoot();
        userPref.put(PREF_KEY, "https://kodejava.org");

        // Below we read back the value we've written in the code above.
        System.out.println("Preferences = "
                + userPref.get(PREF_KEY, PREF_KEY + " was not found."));
    }
}

How do I read user input from console using java.util.Scanner class?

By Wayan in Core API, Util Package 1 Comment

In JDK 1.5 a java.util.Scanner class was introduced to handle user input in console application. This class enable us to read string, integer, long, etc.

package org.kodejava.util;

import java.util.Scanner;

public class ScannerDemo {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Read string input for username
        System.out.print("Username: ");
        String username = scanner.nextLine();

        // Read string input for password
        System.out.print("Password: ");
        String password = scanner.nextLine();

        // Read an integer input for another challenge
        System.out.print("What is 2 + 2: ");
        int result = scanner.nextInt();

        if (username.equals("admin")
                && password.equals("secret") && result == 4) {
            System.out.println("Welcome to Java Application");
        } else {
            System.out.println("Invalid username or password, " +
                    "access denied!");
        }
    }
}

The result of the code snippet:

Username: admin
Password: secret
What is 2 + 2: 4
Welcome to Java Application

How do I use ResourceBundle for i18n?

By Wayan in Core API, Util Package 0 Comment

Creating an application for users in different regions can be hard in terms of the message format for the local region. Java provide a ResourceBundle class that help internationalize our application.

To create resources for i18n (there are 18 letters between the first i and the final n) we need to create a file for each locale our application supported. The file name must be ended in language_COUNTRY.properties. For instance a resource bundle for Locale.UK will be MessagesBundle_en_GB.properties.

When the bundle has been loaded we can use bundle.getString(key) to read specific message from our resource bundle file.

package org.kodejava.util;

import java.util.Locale;
import java.util.ResourceBundle;

public class InternationalizationDemo {

    public static void main(String[] args) {
        // Load resource bundle for Locale.UK locale. The resource 
        // bundle will load the MessagesBundle_en_GB.properties file.
        ResourceBundle bundle =
                ResourceBundle.getBundle("MessagesBundle", Locale.UK);
        System.out.println("Message in " + Locale.UK + ": " +
                bundle.getString("greeting"));

        // Change the default locale to Indonesian and get the default 
        // resource bundle for the current locale.
        Locale.setDefault(new Locale("in", "ID"));
        bundle = ResourceBundle.getBundle("MessagesBundle");
        System.out.println("Message in " + Locale.getDefault() + ": " +
                bundle.getString("greeting"));
    }
}

Below are some example of our resource bundle files, these files should be located in our application classpath to enable the ResourceBundle class to read it.

MessagesBundle_en_GB.properties

greeting=Hello, how are you?

MessagesBundle_in_ID.properties

greeting=Halo, apa kabar?

How do I convert time between timezone?

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

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.TimeZone;

public class TimeZoneExample {
    public static void main(String[] args) {
        // Create a calendar object and set it time based on the local
        // time zone
        Calendar localTime = Calendar.getInstance();
        localTime.set(Calendar.HOUR, 17);
        localTime.set(Calendar.MINUTE, 15);
        localTime.set(Calendar.SECOND, 20);

        int hour = localTime.get(Calendar.HOUR);
        int minute = localTime.get(Calendar.MINUTE);
        int second = localTime.get(Calendar.SECOND);

        // Print the local time
        System.out.printf("Local time  : %02d:%02d:%02d\n", hour, minute, second);

        // Create a calendar object for representing a Germany time zone. Then we
        // wet the time of the calendar with the value of the local time
        Calendar germanyTime = new GregorianCalendar(TimeZone.getTimeZone("Germany"));
        germanyTime.setTimeInMillis(localTime.getTimeInMillis());
        hour = germanyTime.get(Calendar.HOUR);
        minute = germanyTime.get(Calendar.MINUTE);
        second = germanyTime.get(Calendar.SECOND);

        // Print the local time in Germany time zone
        System.out.printf("Germany time: %02d:%02d:%02dn", hour, minute, second);
    }
}

How do I set default Locale?

By Wayan 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