Java Networking

Socket socket = new Socket("localhost", 8080);
InputStream in = socket.getInputStream();
OutputStream out = socket.getOutputStream();

// Simple Client Example
import java.io.*;
import java.net.*;

public class Client {

  public static void main(String[] args) {

    try {

      Socket socket = new Socket("localhost", 5000);

      OutputStream out = socket.getOutputStream();
      PrintWriter writer = new PrintWriter(out, true);

      writer.println("Hello Server");

      socket.close();

    } catch (Exception e) {
      e.printStackTrace();
    }

  }
}

// Simple Server Example
import java.io.*;
import java.net.*;

public class Server {

  public static void main(String[] args) {

    try {

      ServerSocket serverSocket = new ServerSocket(5000);
      System.out.println("Server started...");

      Socket socket = serverSocket.accept();

      BufferedReader reader = new BufferedReader(
        new InputStreamReader(socket.getInputStream())
      );

      System.out.println("Message: " + reader.readLine());

      socket.close();
      serverSocket.close();

    } catch (Exception e) {
      e.printStackTrace();
    }

  }
}

• 1 Communication between computers.
• 2 Uses TCP/IP protocol.
• 3 Supports client-server model.
• 4 Part of java.net package.

• 1 Socket – client connection.
• 2 ServerSocket – server side.
• 3 InetAddress – IP address handling.
• 4 URL – web resource access.

• 1 TCP – reliable connection-based.
• 2 UDP – fast but unreliable.
• 3 Client-server communication.
• 4 Peer-to-peer communication.

• 1 Build distributed applications.
• 2 Enable communication between systems.
• 3 Support real-time applications.
• 4 Used in backend systems.

• 1 Used in chat applications.
• 2 Used in online gaming systems.
• 3 Used in client-server architectures.
• 4 Used in distributed systems.
• 5 SaaS products use Java Networking Basics in services, dashboards, background jobs, and API workflows.
• 6 ERP and banking systems apply Java Networking Basics with validation, logging, review, and rollback plans.
• 7 E-commerce and healthcare platforms use Java Networking Basics carefully because reliability and data correctness matter.

• 1 A Java program first evaluates the surrounding context, then applies the Java Networking Basics rules to the current data.
• 2 The important mental model is input, transformation, result, and failure path.
• 3 In production, the same flow usually sits inside a larger layer such as a controller, service, repository, job, or UI component.

• 1 Choose the simplest implementation first, then measure real workloads.
• 2 Watch for repeated work inside loops, unnecessary allocations, and slow I/O in hot paths.
• 3 Prefer clear data structures and stable APIs before micro-optimizing syntax.

• 1 Treat external input as untrusted until it is validated.
• 2 Avoid hardcoded secrets and never print sensitive values in examples or logs.
• 3 Use established libraries for authentication, encryption, parsing, and database access.

• 1 Not closing sockets properly.
• 2 Ignoring port conflicts.
• 3 Not handling exceptions.
• 4 Blocking server threads.
• 5 Skipping the small working example before adding framework code.
• 6 Ignoring null, empty, duplicate, and boundary inputs.
• 7 Mixing business logic, input handling, and output formatting in one place.
• 8 Using broad error handling that hides the real failure.
• 9 Forgetting to test the behavior after refactoring.
• 10 Adding clever code that future maintainers will struggle to read.

• 1 Always close sockets after use.
• 2 Use multi-threading for servers.
• 3 Handle exceptions properly.
• 4 Use proper port management.
• 5 Start with clear requirements and one minimal working example.
• 6 Use meaningful names that explain business intent.
• 7 Keep examples small enough to debug line by line.
• 8 Validate input at every trust boundary.
• 9 Handle errors explicitly and preserve useful context.
• 10 Prefer simple control flow over deeply nested logic.
• 11 Separate domain logic from I/O and framework code.
• 12 Write tests for normal, boundary, and failure cases.
• 13 Review security assumptions before production use.
• 14 Measure performance before optimizing.
• 15 Document non-obvious decisions close to the code or in project notes.
• 16 Use official documentation when behavior is version-specific.
• 17 Keep dependencies current and remove unused code.
• 18 Avoid hardcoded secrets, credentials, and environment-specific paths.
• 19 Log operational events without exposing sensitive data.
• 20 Design examples so learners can safely modify and rerun them.

• 1 Beginner: rewrite the example with different names and values.
• 2 Intermediate: add validation and handle one expected failure case.
• 3 Advanced: place Java Networking Basics inside a small service-style design with tests.

• 1 Build a small Java console feature that demonstrates Java Networking Basics.
• 2 Accept input, process it with the concept, print a clear result, and handle invalid input.
• 3 Add a README note explaining the design choice and two edge cases you tested.

• 1 If the program does not compile, check spelling, imports, braces, and file/class names first.
• 2 If output is unexpected, print intermediate values and verify each branch of the logic.
• 3 If the design feels complex, reduce it to the smallest working example and add pieces back one at a time.

• 1 Practice Java Networking Basics with a second example from a business domain such as inventory, payroll, banking, or e-commerce.
• 2 Review related Java topics that cover data flow, error handling, testing, and clean design.
• 3 Compare your solution with official documentation and simplify anything you cannot explain clearly.