Java Networking and Design Patterns: Key Concepts

Posted on Mar 31, 2026 in Computers

Java Networking Classes Comparison

System Network Information

This program retrieves the IP and MAC addresses of the system and identifies the IP version (IPv4 or IPv6).

import java.net.*;
import java.util.Enumeration;

public class SystemNetworkInfo {
    public static void main(String[] args) {
        try {
            Enumeration<NetworkInterface> networks = NetworkInterface.getNetworkInterfaces();
            while (networks.hasMoreElements()) {
                NetworkInterface netInt = networks.nextElement();
                if (!netInt.isUp() || netInt.isLoopback()) continue;
                System.out.println("Interface Name: " + netInt.getName());
                byte[] mac = netInt.getHardwareAddress();
                if (mac != null) {
                    System.out.print("MAC Address: ");
                    for (int i = 0; i < mac.length; i++) {
                        System.out.printf("%02X%s", mac[i], (i < mac.length - 1) ? "-" : "");
                    }
                    System.out.println();
                }
                Enumeration<InetAddress> addresses = netInt.getInetAddresses();
                while (addresses.hasMoreElements()) {
                    InetAddress addr = addresses.nextElement();
                    System.out.println("IP Address: " + addr.getHostAddress());
                    if (addr instanceof Inet4Address) System.out.println("Type: IPv4");
                    else if (addr instanceof Inet6Address) System.out.println("Type: IPv6");
                }
                System.out.println("----------------------------");
            }
        } catch (Exception e) { e.printStackTrace(); }
    }
}

Factory Method Pattern

The Factory Method pattern defines an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

Example in Java

• Step 1: Product Interface

interface Shape { void draw(); }

• Step 2: Concrete Classes

class Circle implements Shape { public void draw() { System.out.println("Drawing Circle"); } }
class Rectangle implements Shape { public void draw() { System.out.println("Drawing Rectangle"); } }

• Step 3: Factory Class (Creator)

class ShapeFactory {
    public Shape getShape(String type) {
        if (type == null) return null;
        if (type.equalsIgnoreCase("circle")) return new Circle();
        else if (type.equalsIgnoreCase("rectangle")) return new Rectangle();
        return null;
    }
}

• Step 4: Main Class

public class FactoryMethodExample {
    public static void main(String[] args) {
        ShapeFactory factory = new ShapeFactory();
        Shape s1 = factory.getShape("circle"); s1.draw();
        Shape s2 = factory.getShape("rectangle"); s2.draw();
    }
}

Using DatagramChannel

DatagramChannel is a class in the java.nio.channels package used for UDP communication in Java NIO.

UDP Sender Example

import java.net.*;
import java.nio.*;
import java.nio.channels.*;

public class DatagramSender {
    public static void main(String[] args) throws Exception {
        DatagramChannel channel = DatagramChannel.open();
        String message = "Hello UDP";
        ByteBuffer buffer = ByteBuffer.wrap(message.getBytes());
        InetSocketAddress address = new InetSocketAddress("localhost", 5000);
        channel.send(buffer, address);
        channel.close();
    }
}

UDP Receiver Example

import java.net.*;
import java.nio.*;
import java.nio.channels.*;

public class DatagramReceiver {
    public static void main(String[] args) throws Exception {
        DatagramChannel channel = DatagramChannel.open();
        channel.bind(new InetSocketAddress(5000));
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        channel.receive(buffer);
        buffer.flip();
        byte[] data = new byte[buffer.limit()];
        buffer.get(data);
        System.out.println("Received: " + new String(data));
        channel.close();
    }
}

UDP Echo Client

import java.net.*;

public class UDPEchoClient {
    public static void main(String args[]) throws Exception {
        DatagramSocket socket = new DatagramSocket();
        InetAddress ip = InetAddress.getByName("localhost");
        String msg = "Hello";
        byte[] data = msg.getBytes();
        DatagramPacket sendPacket = new DatagramPacket(data, data.length, ip, 5000);
        socket.send(sendPacket);
        byte[] buffer = new byte[1024];
        DatagramPacket receivePacket = new DatagramPacket(buffer, buffer.length);
        socket.receive(receivePacket);
        String response = new String(receivePacket.getData(), 0, receivePacket.getLength());
        System.out.println("Server: " + response);
        socket.close();
    }
}