Main.java

import java.util.ArrayList;
import java.util.Scanner;

// Student Class for individual student profiles
class Student {
    // Private instance variables for safety
    private String name;
    private String id;
    private int age;
    private double grade;

    // Constructor to set up student variables
    public Student(String name, String id, int age, double grade) {
        this.name = name;
        this.id = id;
        this.age = age;
        this.grade = grade;
    }

    // Getters and Setters to access data safely
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public double getGrade() {
        return grade;
    }

    public void setGrade(double grade) {
        this.grade = grade;
    }

    @Override
    public String toString() {
        return "ID: " + id + " | Name: " + name + " | Age: " + age + " | Grade: " + grade;
    }
}

// StudentManagement Class to handle the main record list using static members
class StudentManagement {
    // Private static variables for shared data
    private static ArrayList<Student> studentList = new ArrayList<>();
    private static int totalStudents = 0;

    // Static method to add a student to the list
    public static void addStudent(Student student) {
        studentList.add(student);
        totalStudents++;
        System.out.println("Success: Student added successfully.");
    }

    // Static method to find a student using their ID
    public static Student getStudent(String id) {
        for (Student s : studentList) {
            if (s.getId().equalsIgnoreCase(id)) {
                return s;
            }
        }
        return null; // Returns null if the ID does not exist
    }

    // Static method to change a student's info
    public static boolean updateStudent(String id, String newName, int newAge, double newGrade) {
        Student student = getStudent(id);
        if (student != null) {
            student.setName(newName);
            student.setAge(newAge);
            student.setGrade(newGrade);
            return true;
        }
        return false;
    }

    // Static getter to read the total student count
    public static int getTotalStudents() {
        return totalStudents;
    }
}

// Main Application Class that runs the menu interface
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        boolean running = true;

        System.out.println("=================================================");
        System.out.println("  Welcome to the Student Record Management System");
        System.out.println("=================================================");

        while (running) {
            System.out.println("\n--- Administrator Menu ---");
            System.out.println("1. Add a New Student");
            System.out.println("2. Update Student Information");
            System.out.println("3. View Student Details");
            System.out.println("4. Exit Application");
            System.out.print("Please enter your choice (1-4): ");

            String choice = scanner.nextLine().trim();

            switch (choice) {
                case "1":
                    System.out.print("Enter Student ID: ");
                    String id = scanner.nextLine().trim();

                    // Check if ID is empty or already in the system
                    if (id.isEmpty()) {
                        System.out.println("Error: Student ID cannot be empty.");
                        break;
                    }
                    if (StudentManagement.getStudent(id) != null) {
                        System.out.println("Error: A student with this ID already exists.");
                        break;
                    }

                    System.out.print("Enter Student Name: ");
                    String name = scanner.nextLine().trim();
                    if (name.isEmpty()) {
                        System.out.println("Error: Student name cannot be empty.");
                        break;
                    }

                    try {
                        System.out.print("Enter Student Age: ");
                        int age = Integer.parseInt(scanner.nextLine().trim());
                        if (age < 0 || age > 120) {
                            System.out.println("Error: Please enter a realistic age.");
                            break;
                        }

                        System.out.print("Enter Student Grade/GPA: ");
                        double grade = Double.parseDouble(scanner.nextLine().trim());
                        if (grade < 0.0 || grade > 4.0) {
                            System.out.println("Error: Grade must be between 0.0 and 4.0.");
                            break;
                        }

                        // Create a new student and save them to the shared list
                        Student newStudent = new Student(name, id, age, grade);
                        StudentManagement.addStudent(newStudent);

                    } catch (NumberFormatException e) {
                        System.out.println("Error: Wrong input. Age must be a whole number and Grade must be a decimal.");
                    }
                    break;

                case "2":
                    System.out.print("Enter the ID of the student to update: ");
                    String updateId = scanner.nextLine().trim();
                    Student existingStudent = StudentManagement.getStudent(updateId);

                    if (existingStudent == null) {
                        System.out.println("Error: Student ID not found.");
                        break;
                    }

                    System.out.println("Current Details -> " + existingStudent);
                    System.out.print("Enter New Name: ");
                    String newName = scanner.nextLine().trim();
                    if (newName.isEmpty()) {
                        System.out.println("Error: Name cannot be empty.");
                        break;
                    }

                    try {
                        System.out.print("Enter New Age: ");
                        int newAge = Integer.parseInt(scanner.nextLine().trim());
                        System.out.print("Enter New Grade/GPA: ");
                        double newGrade = Double.parseDouble(scanner.nextLine().trim());

                        boolean updated = StudentManagement.updateStudent(updateId, newName, newAge, newGrade);
                        if (updated) {
                            System.out.println("Success: Student record updated successfully.");
                        } else {
                            System.out.println("Error: Failed to update the record.");
                        }
                    } catch (NumberFormatException e) {
                        System.out.println("Error: Wrong input type. Update stopped.");
                    }
                    break;

                case "3":
                    System.out.print("Enter Student ID to view details: ");
                    String viewId = scanner.nextLine().trim();
                    Student targetStudent = StudentManagement.getStudent(viewId);

                    if (targetStudent != null) {
                        System.out.println("\n--- Student Record Found ---");
                        System.out.println(targetStudent);
                        System.out.println("Total Tracked Students in System: " + StudentManagement.getTotalStudents());
                    } else {
                        System.out.println("Error: Student ID not found.");
                    }
                    break;

                case "4":
                    running = false;
                    System.out.println("Exiting the application. Goodbye!");
                    break;

                default:
                    System.out.println("Error: Wrong option. Pick a number between 1 and 4.");
            }
        }
        scanner.close();
    }
}