Program to count vowels and consonants in a string in Java

public class VowelConsonantCounter {

    public static void main(String[] args) {
        String text = "Hello World";
        countVowelsAndConsonants(text);

        text = "Java Programming";
        countVowelsAndConsonants(text);
    }

    public static void countVowelsAndConsonants(String str) {
        int vowels = 0;
        int consonants = 0;

        // Convert the string to lowercase to handle both cases easily
        str = str.toLowerCase();

        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);

            // Check if the character is an alphabet
            if (ch >= 'a' && ch <= 'z') {
                if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
                    vowels++;
                } else {
                    consonants++;
                }
            }
        }
        System.out.println("String: \"" + str + "\"");
        System.out.println("Number of vowels: " + vowels);
        System.out.println("Number of consonants: " + consonants);
        System.out.println();
    }
}

public class StringReverser {

    public static void main(String[] args) {
        String originalString1 = "Java";
        String reversedString1 = reverseString(originalString1);
        System.out.println("Original String: " + originalString1);
        System.out.println("Reversed String: " + reversedString1);
        System.out.println();

        String originalString2 = "Programming";
        String reversedString2 = reverseString(originalString2);
        System.out.println("Original String: " + originalString2);
        System.out.println("Reversed String: " + reversedString2);
    }

    public static String reverseString(String str) {
        // Create a StringBuilder object with the input string
        StringBuilder sb = new StringBuilder(str);

        // Use the reverse() method of StringBuilder
        sb.reverse();

        // Convert the StringBuilder back to a String and return it
        return sb.toString();
    }
}

user1:pass1
admin:admin123
test:password

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class LoginSystem {

    private static final String CREDENTIALS_FILE = "credentials.txt";
    private Map<String, String> users;

    public LoginSystem() {
        users = new HashMap<>();
        loadCredentials();
    }

    private void loadCredentials() {
        try (BufferedReader reader = new BufferedReader(new FileReader(CREDENTIALS_FILE))) {
            String line;
            while ((line = reader.readLine()) != null) {
                String[] parts = line.split(":");
                if (parts.length == 2) {
                    users.put(parts[0], parts[1]);
                }
            }
        } catch (IOException e) {
            System.err.println("Error loading credentials file: " + e.getMessage());
            System.err.println("Please ensure '" + CREDENTIALS_FILE + "' exists and is correctly formatted.");
        }
    }

    public boolean authenticate(String username, String password) {
        return users.containsKey(username) && users.get(username).equals(password);
    }

    public static void main(String[] args) {
        LoginSystem loginSystem = new LoginSystem();
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter username: ");
        String username = scanner.nextLine();

        System.out.print("Enter password: ");
        String password = scanner.nextLine();

        if (loginSystem.authenticate(username, password)) {
            System.out.println("Login successful! Welcome, " + username + ".");
        } else {
            System.out.println("Login failed. Invalid username or password.");
        }

        scanner.close();
    }
}

public class Student {
    private String name; // Private instance variable
    private int age;     // Private instance variable

    // Getter for name
    public String getName() {
        return name;
    }

    // Setter for name
    public void setName(String name) {
        // Optional: Add validation logic here
        if (name != null && !name.trim().isEmpty()) {
            this.name = name;
        } else {
            System.out.println("Name cannot be empty.");
        }
    }

    // Getter for age
    public int getAge() {
        return age;
    }

    // Setter for age
    public void setAge(int age) {
        // Optional: Add validation logic here
        if (age > 0 && age < 120) {
            this.age = age;
        } else {
            System.out.println("Invalid age provided.");
        }
    }

    public static void main(String[] args) {
        Student student = new Student();

        // Using setter methods to set values
        student.setName("Alice");
        student.setAge(20);

        // Using getter methods to retrieve values
        System.out.println("Student Name: " + student.getName()); // Output: Student Name: Alice
        System.out.println("Student Age: " + student.getAge());   // Output: Student Age: 20

        // Demonstrate validation
        student.setAge(-5); // Output: Invalid age provided.
        student.setName(""); // Output: Name cannot be empty.
    }
}