Sockets in Java are a mechanism for creating network connections between different processes or machines. A socket is an endpoint for sending or receiving data across a network connection, and Java provides several classes and interfaces for working with sockets.

To use sockets in Java, we need to create a server and a client program. The server program waits for incoming connections and the client program initiates the connection to the server. Here is an example of a simple server program:

import java.net.*;
import java.io.*;

public class Server {
    public static void main(String[] args) {
        try {
            ServerSocket server = new ServerSocket(8000);
            System.out.println("Server started");

            while (true) {
                Socket socket = server.accept();
                System.out.println("Client connected: " + socket);

                DataInputStream input = new DataInputStream(socket.getInputStream());
                String message = input.readUTF();
                System.out.println("Message from client: " + message);

                DataOutputStream output = new DataOutputStream(socket.getOutputStream());
                output.writeUTF("Hello from server");

                socket.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In this example, we create a ServerSocket object on port 8000 and wait for incoming connections using the accept() method. When a client connects, we create a Socket object and get the input and output streams for sending and receiving data. We then read a message from the client using a DataInputStream and send a response using a DataOutputStream. Finally, we close the socket.

Here is an example of a client program that connects to the server:

import java.net.*;
import java.io.*;

public class Client {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 8000);
            System.out.println("Connected to server");

            DataOutputStream output = new DataOutputStream(socket.getOutputStream());
            output.writeUTF("Hello from client");

            DataInputStream input = new DataInputStream(socket.getInputStream());
            String message = input.readUTF();
            System.out.println("Message from server: " + message);

            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In this example, we create a Socket object and connect it to the server using the server’s hostname and port number. We then get the input and output streams and send a message to the server using a DataOutputStream. We read the server’s response using a DataInputStream and close the socket.

Sockets can be used for a wide range of network communication tasks, such as file transfer, chat applications, and remote procedure calls. They provide a flexible and powerful mechanism for creating network connections in Java.

A quick recap of Java