Java Labs Page 10 - Networking, Modules & Modern Features

Lab 28: Networking with Sockets

Expert

Coding Challenge

Your Task: Learn Java networking fundamentals using Socket and ServerSocket for client-server communication.

Detailed Requirements:
1. URL and HTTP connections:
   • URL url = new URL("http://...");
   • HttpURLConnection conn = (HttpURLConnection) url.openConnection();

2. Server Socket:
   • ServerSocket server = new ServerSocket(port);
   • Socket client = server.accept();

3. Client Socket:
   • Socket socket = new Socket(host, port);
   • Use InputStream/OutputStream for communication

4. BufferedReader/PrintWriter for text communication

Expected Output:

--- URL Connection Demo ---
Connecting to: https://api.example.com
Response Code: 200
Content Type: application/json

--- Socket Concepts ---
Server would listen on port: 8080
Client would connect to: localhost:8080

--- InetAddress Demo ---
Localhost: 127.0.0.1
Hostname: localhost

Requirements Checklist

Create URL object

Use HttpURLConnection or URLConnection

Use ServerSocket class

Use Socket class for client

Use InetAddress for IP operations

Handle IOException properly

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

public class NetworkDemo {
    public static void main(String[] args) {
        System.out.println("--- URL Connection Demo ---");
        
        // TODO: Create URL and open connection
        // try {
        //     URL url = new URL("https://api.example.com");
        //     System.out.println("Connecting to: " + url);
        //     
        //     HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        //     conn.setRequestMethod("GET");
        //     
        //     System.out.println("Response Code: " + conn.getResponseCode());
        //     System.out.println("Content Type: " + conn.getContentType());
        //     
        //     conn.disconnect();
        // } catch (IOException e) {
        //     System.out.println("Connection error: " + e.getMessage());
        // }
        
        
        System.out.println("\n--- Socket Concepts ---");
        
        // TODO: Demonstrate socket concepts (don't actually connect)
        // int port = 8080;
        // String host = "localhost";
        // 
        // System.out.println("Server would listen on port: " + port);
        // System.out.println("Client would connect to: " + host + ":" + port);
        // 
        // // ServerSocket example (commented - would block)
        // // ServerSocket serverSocket = new ServerSocket(port);
        // // Socket clientSocket = serverSocket.accept();
        // 
        // // Client Socket example (commented - needs server)
        // // Socket socket = new Socket(host, port);
        // // PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        // // BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        
        
        System.out.println("\n--- InetAddress Demo ---");
        
        // TODO: Use InetAddress to get IP information
        // try {
        //     InetAddress localhost = InetAddress.getLocalHost();
        //     System.out.println("Localhost: " + localhost.getHostAddress());
        //     System.out.println("Hostname: " + localhost.getHostName());
        //     
        //     // Get IP by hostname
        //     InetAddress google = InetAddress.getByName("google.com");
        //     System.out.println("Google IP: " + google.getHostAddress());
        // } catch (UnknownHostException e) {
        //     System.out.println("Host error: " + e.getMessage());
        // }
        
    }
}

Output

// Click "Run Code" to compile and execute

Hints & Tips

• URL: new URL("http://example.com")

• HTTP: (HttpURLConnection) url.openConnection()

• Server: new ServerSocket(port)

• Client: new Socket(host, port)

• IP: InetAddress.getLocalHost()

Progress: 0/6

Score: 0/100

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Lab 29: Java Module System

Expert

Coding Challenge

Your Task: Learn the Java Platform Module System (JPMS) introduced in Java 9 for better encapsulation and dependency management.

Detailed Requirements:
1. Module declaration (module-info.java):
   • module com.myapp { }

2. Export packages:
   • exports com.myapp.api;
   • exports com.myapp.util to com.other;

3. Require dependencies:
   • requires java.sql;
   • requires transitive java.logging;

4. Services:
   • provides MyService with MyServiceImpl;
   • uses MyService;

Expected Output:

--- Java Module System Demo ---

Module Declaration Example:
module com.myapp {
    requires java.base;
    requires java.sql;
    requires transitive java.logging;
    
    exports com.myapp.api;
    exports com.myapp.util to com.other;
    
    opens com.myapp.internal to com.framework;
    
    provides com.myapp.spi.Service with com.myapp.impl.ServiceImpl;
    uses com.myapp.spi.Plugin;
}

Current Module: unnamed module

Requirements Checklist

Declare module with 'module' keyword

Use 'requires' for dependencies

Use 'exports' to expose packages

Use 'opens' for reflection access

Use 'provides...with' for services

Use 'uses' to consume services

public class ModuleDemo {
    public static void main(String[] args) {
        System.out.println("--- Java Module System Demo ---");
        System.out.println();
        
        // TODO: Print module declaration example
        // String moduleDeclaration = """
        //     Module Declaration Example:
        //     module com.myapp {
        //         requires java.base;
        //         requires java.sql;
        //         requires transitive java.logging;
        //         
        //         exports com.myapp.api;
        //         exports com.myapp.util to com.other;
        //         
        //         opens com.myapp.internal to com.framework;
        //         
        //         provides com.myapp.spi.Service with com.myapp.impl.ServiceImpl;
        //         uses com.myapp.spi.Plugin;
        //     }
        //     """;
        // System.out.println(moduleDeclaration);
        
        
        // TODO: Get current module information
        // Module currentModule = ModuleDemo.class.getModule();
        // System.out.println("Current Module: " + 
        //     (currentModule.isNamed() ? currentModule.getName() : "unnamed module"));
        
        
        // TODO: List available modules (example)
        // System.out.println("\nSome JDK Modules:");
        // ModuleLayer.boot().modules().stream()
        //     .map(Module::getName)
        //     .filter(name -> name.startsWith("java."))
        //     .limit(5)
        //     .forEach(name -> System.out.println("  - " + name));
        
    }
}

/*
 * Example module-info.java file:
 * 
 * module com.myapp {
 *     // Dependencies
 *     requires java.base;           // Implicit, always available
 *     requires java.sql;            // Database access
 *     requires transitive java.logging;  // Transitive dependency
 *     
 *     // Expose packages
 *     exports com.myapp.api;        // Public API
 *     exports com.myapp.util to com.other;  // Qualified export
 *     
 *     // Reflection access
 *     opens com.myapp.internal to com.framework;
 *     
 *     // Service Provider Interface
 *     provides com.myapp.spi.Service with com.myapp.impl.ServiceImpl;
 *     uses com.myapp.spi.Plugin;
 * }
 */

Output

// Click "Run Code" to compile and execute

Hints & Tips

• Declare: module com.myapp { }

• Depend: requires java.sql;

• Export: exports com.myapp.api;

• Reflect: opens com.myapp to framework;

• Service: provides X with Y;

Progress: 0/6

Score: 0/100

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Lab 30: Records & Sealed Classes

Expert

Coding Challenge

Your Task: Master modern Java features: Records (Java 14+) for immutable data and Sealed Classes (Java 17+) for restricted inheritance.

Detailed Requirements:
1. Records (immutable data carriers):
   • record Person(String name, int age) { }
   • Auto-generates constructor, getters, equals, hashCode, toString
   • Can add compact constructors and methods

2. Sealed Classes (restricted inheritance):
   • sealed class Shape permits Circle, Rectangle { }
   • Subclasses must be: final, sealed, or non-sealed

3. Pattern matching with sealed classes:
   • Exhaustive switch expressions

Expected Output:

--- Records Demo ---
Person: Person[name=Alice, age=30]
Name: Alice, Age: 30
Equals: true
HashCode match: true

--- Sealed Classes Demo ---
Circle area: 78.54
Rectangle area: 24.00
Triangle area: 6.00

--- Pattern Matching ---
Processing Circle with radius 5.0
Processing Rectangle 4.0 x 6.0
Processing Triangle with base 3.0

Requirements Checklist

Create a record with 'record' keyword

Access record components (auto-getters)

Create sealed class with 'permits'

Use 'final' on permitted subclass

Use 'non-sealed' on permitted subclass

Use pattern matching with instanceof or switch

// TODO: Define a record
// record Person(String name, int age) {
//     // Compact constructor for validation
//     public Person {
//         if (age < 0) throw new IllegalArgumentException("Age cannot be negative");
//     }
//     
//     // Can add methods
//     public String greeting() {
//         return "Hello, I'm " + name;
//     }
// }

// TODO: Define sealed class hierarchy
// sealed class Shape permits Circle, Rectangle, Triangle {
//     abstract double area();
// }
// 
// final class Circle extends Shape {
//     private final double radius;
//     public Circle(double radius) { this.radius = radius; }
//     public double radius() { return radius; }
//     double area() { return Math.PI * radius * radius; }
// }
// 
// final class Rectangle extends Shape {
//     private final double width, height;
//     public Rectangle(double w, double h) { width = w; height = h; }
//     public double width() { return width; }
//     public double height() { return height; }
//     double area() { return width * height; }
// }
// 
// non-sealed class Triangle extends Shape {
//     private final double base, height;
//     public Triangle(double b, double h) { base = b; height = h; }
//     public double base() { return base; }
//     double area() { return 0.5 * base * height; }
// }

public class ModernJavaDemo {
    
    // TODO: Pattern matching method
    // static void processShape(Shape shape) {
    //     if (shape instanceof Circle c) {
    //         System.out.println("Processing Circle with radius " + c.radius());
    //     } else if (shape instanceof Rectangle r) {
    //         System.out.println("Processing Rectangle " + r.width() + " x " + r.height());
    //     } else if (shape instanceof Triangle t) {
    //         System.out.println("Processing Triangle with base " + t.base());
    //     }
    // }
    
    public static void main(String[] args) {
        System.out.println("--- Records Demo ---");
        
        // TODO: Use record
        // Person alice = new Person("Alice", 30);
        // Person alice2 = new Person("Alice", 30);
        // 
        // System.out.println("Person: " + alice);
        // System.out.println("Name: " + alice.name() + ", Age: " + alice.age());
        // System.out.println("Equals: " + alice.equals(alice2));
        // System.out.println("HashCode match: " + (alice.hashCode() == alice2.hashCode()));
        
        
        System.out.println("\n--- Sealed Classes Demo ---");
        
        // TODO: Use sealed classes
        // Shape circle = new Circle(5.0);
        // Shape rect = new Rectangle(4.0, 6.0);
        // Shape tri = new Triangle(3.0, 4.0);
        // 
        // System.out.printf("Circle area: %.2f%n", circle.area());
        // System.out.printf("Rectangle area: %.2f%n", rect.area());
        // System.out.printf("Triangle area: %.2f%n", tri.area());
        
        
        System.out.println("\n--- Pattern Matching ---");
        
        // TODO: Use pattern matching
        // processShape(circle);
        // processShape(rect);
        // processShape(tri);
        
    }
}

Output

// Click "Run Code" to compile and execute

Hints & Tips

• Record: record Point(int x, int y) { }

• Access: point.x() not point.getX()

• Sealed: sealed class X permits A, B { }

• Subclass: final class A extends X { }

• Pattern: if (obj instanceof Type t) { use t }

Progress: 0/6

Score: 0/100

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Java Programming Labs

Networking, Modules & Modern Features - Module 10

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