Advanced Java Programs with Explanation

Here are examples of advanced Java programs, along with explanations:

---

1. Multithreading in Java

This program demonstrates how to use threads in Java.

class MyThread extends Thread {
    public void run() {
        for (int i = 0; i < 5; i++) {
            System.out.println(Thread.currentThread().getName() + " - " + i);
            try {
                Thread.sleep(500); // Pauses execution for 500ms
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

public class MultithreadingExample {
    public static void main(String[] args) {
        MyThread t1 = new MyThread();
        MyThread t2 = new MyThread();

        t1.start();
        t2.start();
    }
}

Explanation:

• MyThread extends Thread: A custom thread class.
• start(): Starts the thread, invoking its run() method.
• Thread.sleep(500): Puts the thread to sleep for 500 milliseconds.

---

2. Reading and Writing Files

This program demonstrates file handling by writing and then reading from a file.

import java.io.*;

public class FileHandling {
    public static void main(String[] args) {
        String filePath = "example.txt";

        // Writing to a file
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(filePath))) {
            writer.write("This is a sample text file.");
            writer.newLine();
            writer.write("File handling in Java is powerful.");
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Reading from a file
        try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• BufferedWriter and FileWriter: Used to write text to a file.
• BufferedReader and FileReader: Used to read text from a file.
• try-with-resources: Ensures that file streams are closed automatically.

---

3. Lambda Expressions

This program demonstrates the use of lambda expressions to simplify functional interfaces.

import java.util.*;

public class LambdaExample {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "Diana");

        // Using a lambda expression to sort the list
        Collections.sort(names, (a, b) -> a.compareTo(b));

        // Using a lambda expression to print each element
        names.forEach(name -> System.out.println(name));
    }
}

Explanation:

• (a, b) -> a.compareTo(b): Lambda function to compare two strings.
• names.forEach: Iterates through the list using a lambda expression.

---

4. Implementing a Singleton Design Pattern

This program shows how to implement the Singleton pattern.

class Singleton {
    private static Singleton instance;

    private Singleton() {
        // Private constructor
    }

    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }

    public void showMessage() {
        System.out.println("Singleton instance invoked!");
    }
}

public class SingletonExample {
    public static void main(String[] args) {
        Singleton singleton = Singleton.getInstance();
        singleton.showMessage();
    }
}

Explanation:

• private static Singleton instance;: Ensures only one instance is created.
• getInstance(): Provides access to the instance.
• private Singleton(): Prevents instantiation from other classes.

---

5. JDBC Connectivity

This program connects to a database using JDBC.

import java.sql.*;

public class JDBCExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/testdb";
        String user = "root";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            System.out.println("Connected to the database!");

            String query = "SELECT * FROM users";
            try (Statement stmt = conn.createStatement();
                 ResultSet rs = stmt.executeQuery(query)) {

                while (rs.next()) {
                    System.out.println("ID: " + rs.getInt("id") +
                                       ", Name: " + rs.getString("name"));
                }
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• DriverManager.getConnection: Establishes a connection to the database.
• Statement and ResultSet: Executes queries and retrieves results.

---

6. Java Streams API

This program demonstrates the use of Streams for functional programming.

import java.util.*;
import java.util.stream.*;

public class StreamsExample {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        // Filtering even numbers and summing them
        int sum = numbers.stream()
                         .filter(n -> n % 2 == 0)
                         .mapToInt(n -> n)
                         .sum();

        System.out.println("Sum of even numbers: " + sum);
    }
}

Explanation:

• stream(): Converts the list to a stream.
• filter: Filters only even numbers.
• mapToInt: Maps each number to an int.
• sum(): Sums all the filtered numbers.

---

7. Custom Exception

This program demonstrates how to create and throw a custom exception.

class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

public class CustomExceptionExample {
    public static void main(String[] args) {
        try {
            checkValue(10);
        } catch (CustomException e) {
            System.out.println(e.getMessage());
        }
    }

    public static void checkValue(int value) throws CustomException {
        if (value < 20) {
            throw new CustomException("Value is less than 20!");
        }
    }
}

Explanation:

• CustomException extends Exception: Creates a custom exception class.
• throw new CustomException: Throws the custom exception.

---

These programs demonstrate advanced Java concepts such as multithreading, file handling, design patterns, JDBC, Streams API, and custom exceptions. Let me know if you'd like more examples! 😊