How do I get a list of weekday names?

By Wayan in Core API, Text Package 0 Comment

The example code below helps you to get all weekday names as an array of string. The first method, getWeekdays() return the full name string while the second method getShortWeekdays() return the short name of the weekday.

package org.kodejava.text;

import java.text.DateFormatSymbols;

public class WeekdayNames {
    public static void main(String[] args) {
        DateFormatSymbols dfs = new DateFormatSymbols();

        String[] weekdays = dfs.getWeekdays();
        for (String weekday : weekdays) {
            System.out.println("weekday = " + weekday);
        }

        String[] shortWeekdays = dfs.getShortWeekdays();
        for (String shortWeekday : shortWeekdays) {
            System.out.println("shortWeekday = " + shortWeekday);
        }
    }
}

The results of the code above are:

weekday = 
weekday = Sunday
weekday = Monday
weekday = Tuesday
weekday = Wednesday
weekday = Thursday
weekday = Friday
weekday = Saturday
shortWeekday = 
shortWeekday = Sun
shortWeekday = Mon
shortWeekday = Tue
shortWeekday = Wed
shortWeekday = Thu
shortWeekday = Fri
shortWeekday = Sat

How do I get a list of month names?

By Wayan in Core API, Text Package 6 Comments

The example code below helps you to get all month names as an array of String. The first method, getMonths() return the full name string while the second method getShortMonths() return the short name of the month.

package org.kodejava.text;

import java.text.DateFormatSymbols;
import java.util.Locale;

public class MonthNames {
    public static void main(String[] args) {
        String[] months = new DateFormatSymbols().getMonths();
        for (String month : months) {
            System.out.println("month = " + month);
        }

        String[] shortMonths = new DateFormatSymbols().getShortMonths();
        for (String shortMonth : shortMonths) {
            System.out.println("shortMonth = " + shortMonth);
        }

        DateFormatSymbols dfs = new DateFormatSymbols(Locale.GERMANY);
        String[] germanyMonths = dfs.getMonths();
        for (String germanyMonth : germanyMonths) {
            System.out.println("germanyMonth = " + germanyMonth);
        }

        String[] germanyShortMonths = dfs.getShortMonths();
        for (String germanyShortMonth : germanyShortMonths) {
            System.out.println("germanyShortMonth = "
                    + germanyShortMonth);
        }
    }
}

The results of the code above are:

month = January
month = February
...
month = December
month = 
shortMonth = Jan
shortMonth = Feb
...
shortMonth = Dec
shortMonth = 
germanyMonth = Januar
germanyMonth = Februar
...
germanyMonth = Dezember
germanyMonth = 
germanyShortMonth = Jan
germanyShortMonth = Feb
...
germanyShortMonth = Dez
germanyShortMonth =

How do I convert primitive boolean type into Boolean object?

By Wayan in Core API, Lang Package 0 Comment

The following code snippet demonstrate how to use the Boolean.valueOf() method to convert primitive boolean value or a string into Boolean object. This method will return the corresponding Boolean object of the given primitive boolean value.

When a string value is passed to this method it will return Boolean.TRUE when the string is not null, and the value is equal, ignoring case, to the string "true". Otherwise, it will return Boolean.FALSE object.

package org.kodejava.lang;

public class BooleanValueOfExample {
    public static void main(String[] args) {
        boolean b = true;
        Boolean bool = Boolean.valueOf(b);
        System.out.println("bool = " + bool);

        // Here we test the conversion, which is likely unnecessary. But
        // here is shown the boolean true is equals to Boolean.TRUE static
        // variable and of course you can guest the boolean false value is
        // equals to Boolean.FALSE
        if (bool.equals(Boolean.TRUE)) {
            System.out.println("bool = " + bool);
        }

        // On the line below we convert a string to Boolean, it returns
        // true if and only if the string is equals to "true" otherwise it
        // returns false
        String s = "false";
        Boolean bools = Boolean.valueOf(s);
        System.out.println("bools = " + bools);

        String f = "abc";
        Boolean abc = Boolean.valueOf(f);
        System.out.println("abc = " + abc);
    }
}

The code snippet will print the following output:

bool = true
bool = true
boolS = false
abc = false

Can I create a boolean variable from string?

By Wayan in Core API, Lang Package 0 Comment

To convert a string into boolean we can use the Boolean.parseBoolean(String) method. If we pass a non null value that equals to true, ignoring case, this method will return true value. Given other values it will return a false boolean value.

package org.kodejava.lang;

public class BooleanParseExample {
    public static void main(String[] args) {
        // Parsing string "true" will result boolean true
        boolean boolA = Boolean.parseBoolean("true");
        System.out.println("boolA = " + boolA);

        // Parsing string "TRUE" also result boolean true, as the
        // parsing method is case insensitive
        boolean boolB = Boolean.parseBoolean("TRUE");
        System.out.println("boolB = " + boolB);

        // The operation below will return false, as Yes is not
        // a valid string value for boolean expression
        boolean boolC = Boolean.parseBoolean("Yes");
        System.out.println("boolC = " + boolC);

        // Parsing a number is also not a valid expression so the
        // parsing method return false
        boolean boolD = Boolean.parseBoolean("1");
        System.out.println("boolD = " + boolD);
    }
}

The code snippet above will print the following output:

boolA = true
boolB = true
boolC = false
boolD = false

How do I delete a file in Java?

By Wayan in Core API, IO 0 Comment

In this example you will see how to delete a file in Java. To delete a file we start by creating a File object that represent the file to be deleted. We use the exists() method to check if the file is exists before we try to delete it.

To delete the file we call the delete() method of the File object. If the file was successfully deleted the method will return a boolean true result, otherwise it will return false. Let’s try the code snippet below.

package org.kodejava.io;

import java.io.File;

public class FileDeleteExample {
    public static void main(String[] args) {
        // When want to delete a file named readme.txt
        File file = new File("write.txt");

        // Checks if the file is exists before deletion.
        if (file.exists()) {
            System.out.println("Deleting " + file.getAbsolutePath());
            // Use the delete method to delete the given file.
            boolean deleted = file.delete();
            if (deleted) {
                System.out.println(file.getAbsolutePath() + " was deleted.");
            }
        } else {
            System.out.println(file.getAbsolutePath() + " not found.");
        }
    }
}

How do I get IP address of localhost?

By Wayan in Core API, Networking 0 Comment

The example here show you how to get an IP or host address using the java.net.InetAddress class. To get an instance of InetAddress we call a static method of this class, the method is getLocalHost(), which return the local host address. Next, to get the IP address we can call the getHostAddress() method.

package org.kodejava.net;

import java.net.InetAddress;
import java.net.UnknownHostException;

public class LocalHostIpAddress {
    public static void main(String[] args) {
        try {
            InetAddress address = InetAddress.getLocalHost();
            String ip = address.getHostAddress();

            System.out.println("IP Address = " + ip);
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }
}

The result of this code snippet:

IP Address = 30.30.30.60

How do I create an empty collection object?

By Wayan in Core API, Util Package 3 Comments

Sometimes you need to return an empty collection from your Java methods. The java.util.Collections utility class have three different static constants for creating empty List, Set and Map.

  • Collections.EMPTY_LIST
  • Collections.EMPTY_SET
  • Collections.EMPTY_MAP

There are also methods when you want to create type-safe empty collections.

  • Collections.emptyList()
  • Collections.emptySet()
  • Collections.emptyMap()

Bellow it the code example.

package org.kodejava.util;

import java.util.*;

public class EmptyCollectionDemo {
    public static void main(String[] args) {
        List list = Collections.EMPTY_LIST;
        System.out.println("list.size()  = " + list.size());
        Set set = Collections.EMPTY_SET;
        System.out.println("set.size()   = " + set.size());
        Map map = Collections.EMPTY_MAP;
        System.out.println("map.size()   = " + map.size());

        // For the type-safe example use the following methods.
        List<String> strings = Collections.emptyList();
        System.out.println("strings.size = " + strings.size());

        Set<Long> longs = Collections.emptySet();
        System.out.println("longs.size() = " + longs.size());

        Map<String, Date> dates = Collections.emptyMap();
        System.out.println("dates.size() = " + dates.size());
    }
}

The output are:

list.size()  = 0
set.size()   = 0
map.size()   = 0
strings.size = 0
longs.size() = 0
dates.size() = 0

How do I read entries in a zip / compressed file?

By Wayan in Zip and GZIP 0 Comment 
package org.kodejava.util.zip;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Enumeration;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;

public class ZipFileExample {
    public static void main(String[] args) {
        try {
            // Create an instance of ZipFile to read a zip file
            // called sample.zip
            ZipFile zip = new ZipFile(new File("data.zip"));

            // Here we start to iterate each entry inside
            // sample.zip
            for (Enumeration<?> e = zip.entries(); e.hasMoreElements(); ) {
                // Get ZipEntry which is a file or a directory
                ZipEntry entry = (ZipEntry) e.nextElement();

                // Get some information about the entry such as
                // file name, its size.
                System.out.println("File name: " + entry.getName()
                    + "; size: " + entry.getSize()
                    + "; compressed size: "
                    + entry.getCompressedSize());
                System.out.println();

                // Now we want to get the content of this entry.
                // Get the InputStream, we read through the input
                // stream until all the content is read.
                InputStream is = zip.getInputStream(entry);
                InputStreamReader isr = new InputStreamReader(is);

                char[] buffer = new char[1024];
                while (isr.read(buffer, 0, buffer.length) != -1) {
                    String s = new String(buffer);
                    // Here we just print out what is inside the
                    // buffer.
                    System.out.println(s.trim());
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

What is Autoboxing?

By Wayan in Basic, Core API 0 Comment

Autoboxing is a new feature offered in the Tiger (1.5) release of Java SDK. In short auto boxing is a capability to convert or cast between object wrappers (Integer, Long, etc) and their primitive types.

Previously when placing primitive data into one of the Java Collection Framework object we have to wrap it to an object because the collection cannot work with primitive data. Also, when calling a method that requires an instance of object rather than an int or long, we have to convert it too.

Now, starting from version Java 1.5 we have a new feature in the Java Language which automate this process, its call the Autoboxing. When we place an int value into a collection, such as List, it will be converted into an Integer object behind the scene. When we read it back, it will automatically convert to the primitive type. In most way this simplifies the way we code, no need to do an explicit object casting.

Here an example how it will look like using the Autoboxing feature:

package org.kodejava.basic;

import java.util.HashMap;
import java.util.Map;

public class Autoboxing {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();

        // Here we put an int into the Map, and it accepted
        // as it will be autoboxed or converted into the wrapper
        // of this type, in this case the Integer object.
        map.put("Age", 25);

        // Here we can just get the value from the map, no need
        // to cast it from Integer to int.
        int age = map.get("Age");

        // Here we simply do the math on the primitive type
        // and got the result as an Integer.
        Integer newAge = age + 10;
    }
}

How do I use Java NIO to copy file?

By Wayan in Core API, IO 0 Comment

The following code snippet show you how to copy a file using the NIO API. The NIO (New IO) API is in the java.nio.* package. It requires at least Java 1.4 because the API was first included in this version. The JAVA NIO is a block based IO processing, instead of a stream based IO which is the old version IO processing in Java.

package org.kodejava.io;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.channels.FileChannel;
import java.nio.ByteBuffer;

public class CopyFileExample {
    public static void main(String[] args) throws Exception {
        String source = "medical-report.txt";
        String destination = "medical-report-final.txt";

        FileInputStream fis = new FileInputStream(source);
        FileOutputStream fos = new FileOutputStream(destination);

        FileChannel inputChannel = fis.getChannel();
        FileChannel outputChannel = fos.getChannel();

        // Create a buffer with 1024 size for buffering data
        // while copying from source file to destination file.
        // To create the buffer here we used a static method
        // ByteBuffer.allocate()
        ByteBuffer buffer = ByteBuffer.allocate(1024);

        // Here we start to read the source file and write it
        // to the destination file. We repeat this process
        // until the read method of input stream channel return
        // nothing (-1).
        while (true) {
            // Read a block of data and put it in the buffer
            int read = inputChannel.read(buffer);

            // Did we reach the end of the channel? if yes
            // jump out the while-loop
            if (read == -1) {
                break;
            }

            // flip the buffer
            buffer.flip();

            // write to the destination channel and clear the buffer.
            outputChannel.write(buffer);
            buffer.clear();
        }
    }
}