How do I get IP address of localhost?

By I Wayan Saryada 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 I Wayan Saryada 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

What is Autoboxing?

By I Wayan Saryada 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 I Wayan Saryada 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();
        }
    }
}

How do I split a string?

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

Prior to Java 1.4 we use java.util.StringTokenizer class to split a tokenized string, for example a comma separated string. Starting from Java 1.4 and later the java.lang.String class introduce a String.split(String regex) method that simplify this process.

Below is a code snippet how to do it.

package org.kodejava.lang;

import java.util.Arrays;

public class StringSplit {
    public static void main(String[] args) {
        String data = "1,Diego Maradona,Footballer,Argentina";
        String[] items = data.split(",");

        // Iterates the array to print it out.
        for (String item : items) {
            System.out.println("item = " + item);
        }

        // Or simply use Arrays.toString() when print it out.
        System.out.println("item = " + Arrays.toString(items));
    }
}

The result of the code snippet:

item = 1
item = Diego Maradona
item = Footballer
item = Argentina
item = [1, Diego Maradona, Footballer, Argentina]