How do I get number of available screens?

By Wayan in AWT, Core API 0 Comment

This code shows how to get number of available screen devices on the local machine or local graphics environment. We obtain the number of screens by getting the length of array returned by GraphicsEnvironment.getScreenDevices() method.

This process can produce a HeadlessException to happen if we try to run this code on a machine that doesn’t have a screen device with it.

package org.kodejava.awt;

import java.awt.GraphicsEnvironment;
import java.awt.GraphicsDevice;
import java.awt.HeadlessException;

public class GettingNumberOfScreen {
    public static void main(String[] args) {
        try {
            // Get local graphics environment
            GraphicsEnvironment env = GraphicsEnvironment.getLocalGraphicsEnvironment();

            // Returns an array of all the screen GraphicsDevice objects.
            GraphicsDevice[] devices = env.getScreenDevices();

            int numberOfScreens = devices.length;
            System.out.println("Number of available screens = " + numberOfScreens);
        } catch (HeadlessException e) {
            // We'll get here if no screen devices was found.
            e.printStackTrace();
        }
    }
}

The output of the code snippet above:

Number of available screens = 2

How do I format a message that contains number information?

By Wayan in Core API, Text Package 0 Comment

This example show you how to use java.text.MessageFormat class to format a message that contains numbers.

package org.kodejava.text;

import java.text.MessageFormat;
import java.util.Locale;

public class MessageFormatNumber {
    public static void main(String[] args) {

        // Set the Locale for the MessageFormat.
        Locale.setDefault(Locale.US);

        // Use the default formatting for number.
        String message = MessageFormat.format("This is a {0} and {1} numbers",
                10, 75);
        System.out.println(message);

        // This line has the same format as above.
        message = MessageFormat.format("This is a {0,number} and {1,number} " +
                "numbers", 10, 75);
        System.out.println(message);

        // Format a number with 2 decimal digits.
        message = MessageFormat.format("This is a formatted {0, number,#.##} " +
                "and {1, number,#.##} numbers", 25.7575, 75.2525);
        System.out.println(message);

        // Format a number as currency.
        message = MessageFormat.format("This is a formatted currency " +
                        "{0,number,currency} and {1,number,currency} numbers",
                25.7575, 25.7575);
        System.out.println(message);

        // Format numbers in percentage.
        message = MessageFormat.format("This is a formatted percentage " +
                "{0,number,percent} and {1,number,percent} numbers", 0.10, 0.75);
        System.out.println(message);
    }
}

The result of the program are the following lines:

This is a 10 and 75 numbers
This is a 10 and 75 numbers
This is a formatted 25.76 and 75.25 numbers
This is a formatted currency $25.76 and $25.76 numbers
This is a formatted percentage 10% and 75% numbers

How do I format a message that contains time information?

By Wayan in Core API, Text Package 0 Comment

Here we demonstrate how to use the java.text.MessageFormat class to format a message contains time information.

package org.kodejava.text;

import java.util.Date;
import java.util.Calendar;
import java.util.Locale;
import java.text.MessageFormat;

public class MessageFormatTime {
    public static void main(String[] args) {
        Date today = new Date();
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.HOUR, 7);

        Date next7Hours = calendar.getTime();

        // We want the message to be is Locale.US
        Locale.setDefault(Locale.US);

        // Format a time including date information.
        String message = MessageFormat.format("Now is {0} and the next " +
                "7 hours is {1}", today, next7Hours);
        System.out.println(message);

        // Format a time and display only the time portion
        message = MessageFormat.format("Now is {0, time} and the next " +
                "7 hours is {1, time}", today, next7Hours);
        System.out.println(message);

        // Format a time using a short format (e.g. HH:mm am/pm)
        message = MessageFormat.format("Now is {0, time, short} and " +
                "the next 7 hours is {1, time, short}", today, next7Hours);
        System.out.println(message);

        // Format a time using a medium format (eg. HH:mm:ss am/pm).
        message = MessageFormat.format("Now is {0, time, medium} and " +
                "the next 7 hours is {1, time, medium}", today, next7Hours);
        System.out.println(message);

        // Format a time using a long format (e.g. HH:mm:ss am/pm TIMEZONE).
        message = MessageFormat.format("Now is {0, time, long} and the " +
                "next 7 hours is {1, time, long}", today, next7Hours);
        System.out.println(message);

        // Format a time using a full format (e.g. HH:mm:ss am/pm TIMEZONE).
        message = MessageFormat.format("Now is {0, time, full} and the " +
                "next 7 hours is {1, time, full}", today, next7Hours);
        System.out.println(message);

        // Format a time using a custom pattern.
        message = MessageFormat.format("Now is {0, time, HH:mm:ss.sss} " +
                "and the next 7 hours is {1, time, HH:mm:ss.sss}", today, next7Hours);
        System.out.println(message);
    }
}

The above program produces:

Now is 10/8/21, 9:38 PM and the next 7 hours is 10/9/21, 4:38 AM
Now is 9:38:10 PM and the next 7 hours is 4:38:10 AM
Now is 9:38 PM and the next 7 hours is 4:38 AM
Now is 9:38:10 PM and the next 7 hours is 4:38:10 AM
Now is 9:38:10 PM CST and the next 7 hours is 4:38:10 AM CST
Now is 9:38:10 PM China Standard Time and the next 7 hours is 4:38:10 AM China Standard Time
Now is  21:38:10.010 and the next 7 hours is  04:38:10.010

How do I format a message that contains date information?

By Wayan in Core API, Text Package 0 Comment

This example demonstrate how you can use the java.text.MessageFormat class to format a message with a date information in it.

package org.kodejava.text;

import java.util.Date;
import java.util.Calendar;
import java.util.Locale;
import java.text.MessageFormat;

public class MessageFormatDate {
    public static void main(String[] args) {
        Date today = new Date();
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.DATE, 7);

        Date nextWeek = calendar.getTime();

        // We want the message to be is Locale.US
        Locale.setDefault(Locale.US);

        // Format a date, the time value is included
        String message = MessageFormat.format("Today is {0} and next " +
                "week is {1}", today, nextWeek);
        System.out.println(message);

        // Format a date and display only the date portion
        message = MessageFormat.format("Today is {0,date} and next " +
                "week is {1,date}", today, nextWeek);
        System.out.println(message);

        // Format a date using a short format (e.g. dd/MM/yyyy)
        message = MessageFormat.format("Today is {0,date,short} and " +
                "next week is {1,date,short}", today, nextWeek);
        System.out.println(message);

        // Format a date using a medium format, it displays the month long-name,
        // but using a two digit date and year.
        message = MessageFormat.format("Today is {0,date,medium} and " +
                "next week is {1,date,medium}", today, nextWeek);
        System.out.println(message);

        // Format a date using a long format, two digit for date, a long month
        // name and a four digit year.
        message = MessageFormat.format("Today is {0,date,long} and " +
                "next week is {1,date,long}", today, nextWeek);
        System.out.println(message);

        // Format a date using a full format, the same as above plus a full day
        // name.
        message = MessageFormat.format("Today is {0,date,full} and " +
                "next week is {1,date,full}", today, nextWeek);
        System.out.println(message);

        // Format a date using a custom pattern.
        message = MessageFormat.format("Today is {0,date,dd-MM-yyyy} and " +
                "next week is {1,date,dd-MM-yyyy}", today, nextWeek);
        System.out.println(message);
    }
}

The above program produces:

Today is 10/8/21, 9:35 PM and next week is 10/15/21, 9:35 PM
Today is Oct 8, 2021 and next week is Oct 15, 2021
Today is 10/8/21 and next week is 10/15/21
Today is Oct 8, 2021 and next week is Oct 15, 2021
Today is October 8, 2021 and next week is October 15, 2021
Today is Friday, October 8, 2021 and next week is Friday, October 15, 2021
Today is 08-10-2021 and next week is 15-10-2021

How do I detect non-ASCII characters in string?

By Wayan in Core API, IO 0 Comment

The code below detect if a given string has a non ASCII characters in it. We use the CharsetDecoder class from the java.nio package to decode string to be a valid US-ASCII charset.

package org.kodejava.io;

import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharacterCodingException;
import java.nio.CharBuffer;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;

public class NonAsciiValidation {
    public static void main(String[] args) {
        // This string contains a non ASCII character which will produce exception
        // in this program. While the second string has a valid ASCII only characters.
        byte[] invalidBytes = "Copyright © 2021 Kode Java Org".getBytes();
        byte[] validBytes = "Copyright (c) 2021 Kode Java Org".getBytes();

        // Returns a charset object for the named charset.
        CharsetDecoder decoder = StandardCharsets.US_ASCII.newDecoder();
        try {
            CharBuffer buffer = decoder.decode(ByteBuffer.wrap(validBytes));
            System.out.println(Arrays.toString(buffer.array()));

            buffer = decoder.decode(ByteBuffer.wrap(invalidBytes));
            System.out.println(Arrays.toString(buffer.array()));
        } catch (CharacterCodingException e) {
            System.err.println("The information contains a non ASCII character(s).");
            e.printStackTrace();
        }
    }
}

Below is the result of the program:

[C, o, p, y, r, i, g, h, t,  , (, c, ),  , 2, 0, 2, 1,  , K, o, d, e,  , J, a, v, a,  , O, r, g]
The information contains a non ASCII character(s).
java.nio.charset.MalformedInputException: Input length = 1
    at java.base/java.nio.charset.CoderResult.throwException(CoderResult.java:274)
    at java.base/java.nio.charset.CharsetDecoder.decode(CharsetDecoder.java:820)
    at org.kodejava.io.NonAsciiValidation.main(NonAsciiValidation.java:23)

How do I create temporary file?

By Wayan in Core API, IO 0 Comment

A temporary file can be created by using java.io.File.createTempFile() method. It accepts the prefix, suffix and the path where the file will be stored. When no path is specified it will use the platform default temporary folder.

The name of the temporary file will be in the form of prefix plus five or more random characters plus the suffix. When the suffix is null a default .tmp will be used for suffix.

package org.kodejava.io;

import java.io.File;
import java.io.BufferedWriter;
import java.io.FileWriter;

public class TemporaryFileDemo {
    public static void main(String[] args) throws Exception {
        // Create a temporary file userlist.txt in the default platform
        // temporary folder / directory. We can get the platform temporary
        // folder using System.getProperty("java.io.tmpdir")
        File user = File.createTempFile("userlist", ".txt");

        // Delete the file when the virtual machine is terminated.
        user.deleteOnExit();

        // Create a temporary file data.txt in the user specified folder.
        File data = File.createTempFile("data", ".txt", new File("F:/Temp/Data"));
        data.deleteOnExit();

        // Write data into temporary file
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(data))) {
            writer.write("750101,2008-01-01,BLUE,CAR");
            writer.write("750102,2008-09-06,RED,CAR");
            writer.write("750103,2008-05-01,GREEN,CAR");
            writer.write("750104,2008-06-08,YELLOW,CAR");
        }
    }
}

How do I add hours, minutes or seconds to a date?

By Wayan in Core API, Util Package 0 Comment

This example shows you how to add or subtract hours, minutes or seconds to a date using the java.util.Calendar object.

package org.kodejava.util;

import java.util.Calendar;

public class DateAddSubtract {
    public static void main(String[] args) {
        // Gets a calendar using the default time zone and locale. The
        // Calendar returned is based on the current time in the default
        // time zone with the default locale.
        Calendar calendar = Calendar.getInstance();
        System.out.println("Original = " + calendar.getTime());

        // Subtract 2 hour from the current time
        calendar.add(Calendar.HOUR, -2);

        // Add 30 minutes to the calendar time
        calendar.add(Calendar.MINUTE, 30);

        // Add 300 seconds to the calendar time
        calendar.add(Calendar.SECOND, 300);
        System.out.println("Updated  = " + calendar.getTime());
    }
}

The output of the code snippet:

Original = Wed Oct 06 19:47:53 CST 2021
Updated  = Wed Oct 06 18:22:53 CST 2021

How do I format date using a locale based format?

By Wayan in Core API, Text Package 0 Comment

The code below demonstrate how to format date information for a specific locale. In the example utilize the java.text.SimpleDateFormat class.

package org.kodejava.text;

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

public class FormatDateLocale {
    public static void main(String[] args) {
        // Defines an array of Locale we are going to use for
        // formatting date information.
        Locale[] locales = new Locale[] {
            Locale.JAPAN,
            Locale.CHINA,
            Locale.KOREA,
            Locale.TAIWAN,
            Locale.ITALY,
            Locale.FRANCE,
            Locale.GERMAN
        };

        // Get an instance of current date time
        Date today = new Date();

        // Iterates the entire Locale defined above and create a long
        // formatted date using the SimpleDateFormat.getDateInstance()
        // with the format, the Locale and the date information.
        for (Locale locale : locales) {
            System.out.printf("Date format in %s = %s%n",
                locale.getDisplayName(), SimpleDateFormat.getDateInstance(
                    SimpleDateFormat.LONG, locale).format(today));
        }
    }
}

The result of our code are:

Date format in Japanese (Japan) = 2021年10月6日
Date format in Chinese (China) = 2021年10月6日
Date format in Korean (South Korea) = 2021년 10월 6일
Date format in Chinese (Taiwan) = 2021年10月6日
Date format in Italian (Italy) = 6 ottobre 2021
Date format in French (France) = 6 octobre 2021
Date format in German = 6. Oktober 2021

How do I execute external command and obtain the result?

By Wayan in Core API, Lang Package 0 Comment

This example demonstrate how to execute an external command from Java and obtain the result of the command. Here we simply execute a Linux ls -al command on the current working directory and display the result.

package org.kodejava.lang;

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ProcessResult {
    public static void main(String[] args) {
        try {
            Process process = Runtime.getRuntime().exec("ls -al");

            // Wait for this process to finish or terminated
            process.waitFor();

            // Get process exit value
            int exitValue = process.exitValue();
            System.out.println("exitValue = " + exitValue);

            // Read the result of the ls -al command by reading the
            // process's input stream
            InputStreamReader is = new InputStreamReader(process.getInputStream());
            BufferedReader reader = new BufferedReader(is);
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Below is our program result:

exitValue = 0
total 64
drwxr-xr-x  20 wsaryada  staff   680 Aug  7 14:13 .
drwxr-xr-x   4 wsaryada  staff   136 Jun 18 00:33 ..
-rw-r--r--@  1 wsaryada  staff  6148 Jun 29 14:04 .DS_Store
-rw-r--r--   1 wsaryada  staff   267 May 19 20:47 .editorconfig
drwxr-xr-x  16 wsaryada  staff   544 Aug 10 08:34 .git
-rw-r--r--   1 wsaryada  staff  1535 May 19 20:47 .gitignore
drwxr-xr-x  15 wsaryada  staff   510 Aug 10 08:34 .idea
-rw-r--r--   1 wsaryada  staff  1313 May 19 20:47 LICENSE
-rw-r--r--   1 wsaryada  staff   101 May 19 20:47 README.md
drwxr-xr-x   5 wsaryada  staff   170 Jul 28 23:11 kodejava-basic
drwxr-xr-x   6 wsaryada  staff   204 Jun 30 14:22 kodejava-commons
drwxr-xr-x   6 wsaryada  staff   204 Jul 27 15:32 kodejava-lang-package
drwxr-xr-x@  5 wsaryada  staff   170 Jun 16 20:49 kodejava-mail
drwxr-xr-x   6 wsaryada  staff   204 Aug  7 17:22 kodejava-mybatis
drwxr-xr-x   5 wsaryada  staff   170 Jul 20 10:36 kodejava-poi
-rw-r--r--   1 wsaryada  staff   669 Jun  2 14:29 kodejava-project.iml
drwxr-xr-x   7 wsaryada  staff   238 Jun 26 21:52 kodejava-swing
drwxr-xr-x   6 wsaryada  staff   204 Aug  3 15:06 kodejava-util-package
drwxr-xr-x   6 wsaryada  staff   204 Jun 30 15:09 maven-helloworld
-rw-r--r--   1 wsaryada  staff  1622 Aug  7 14:13 pom.xml

How do I get the path from where a class is loaded?

By Wayan in Core API, Lang Package 0 Comment

This examples shows how to get a path name or location from where our class is loaded.

package org.kodejava.lang;

public class CodeSourceLocation {
    public static void main(String[] args) {
        CodeSourceLocation csl = new CodeSourceLocation();
        csl.getCodeSourceLocation();
    }

    private void getCodeSourceLocation() {
        // The location from where the class is loaded.
        System.out.println("Code source location: " +
            getClass().getProtectionDomain().getCodeSource().getLocation());
    }
}

The code snippet print the following output:

Code source location: file:/F:/Wayan/Kodejava/kodejava-example/kodejava-lang/target/classes/