Networking: Internet Addressing and the InetAddress Class

Internet Addressing

Every device on a TCP/IP network is identified by an IP address:

A port number (0–65535) identifies a specific process/service on a host. Together, IP address + port form a socket address (e.g., 192.168.1.10:8080).

The java.net Package

Java's java.net package provides classes for network programming: InetAddress, Socket, ServerSocket, URL, URLConnection, DatagramSocket, and DatagramPacket.

The InetAddress Class

InetAddress represents an IP address (IPv4 or IPv6) and encapsulates the corresponding hostname. It has no public constructor — objects are created only through factory methods.

Factory Methods (static)

Instance Methods

Example

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

public class InetAddressDemo {
    public static void main(String[] args) throws UnknownHostException {
        // Factory method: resolve by hostname
        InetAddress site = InetAddress.getByName("www.example.com");
        System.out.println("Host: " + site.getHostName());
        System.out.println("IP:   " + site.getHostAddress());

        // Factory method: local machine
        InetAddress local = InetAddress.getLocalHost();
        System.out.println("Local host: " + local);

        // All addresses for a domain
        InetAddress[] all = InetAddress.getAllByName("www.example.com");
        for (InetAddress addr : all) {
            System.out.println("Resolved: " + addr.getHostAddress());
        }
    }
}

Key Takeaway: InetAddress is the foundation of Java networking — it resolves hostnames to IP addresses via factory methods (since there is no public constructor) and exposes address details via instance methods. Every socket-based class (Socket, ServerSocket, DatagramSocket) relies on it internally.