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import java.io.*;
import java.util.*;

class Main {
    public static void main(String[] args) throws Exception {
        System.out.println("Welcome to Student's Data Management System");
        System.out.println();

        Scanner sc = new Scanner(System.in);

        String username = "a";
        int password = 1;

        System.out.print("Enter Username: ");
        String user = sc.next();

        System.out.print("Enter password: ");
        int pass = sc.nextInt();

        int c = 0;

        while (c == 0) {
            if (pass == password && user.equals(username)) {
                System.out.println("Log in Successful");

                int choice = -1;
                ArrayList<Student> A = new ArrayList<>();
                File file = new File("std.txt");
                ObjectInputStream input = null;
                ObjectOutputStream output = null;
                ListIterator<Student> list = null;

                if (file.exists()) {
                    try {
                        input = new ObjectInputStream(new FileInputStream(file));
                        A = (ArrayList<Student>) input.readObject();
                        input.close();
                    } catch (IOException | ClassNotFoundException e) {
                        e.printStackTrace();
                    }
                } else {
                    System.out.println("Creating a new file.");
                    file.createNewFile();
                }

                do {
                    System.out.println("1. Add");
                    System.out.println("2. Display");
                    System.out.println("3. Search");
                    System.out.println("4. Delete");
                    System.out.println("5. Update");
                    System.out.println("0. Exit");
                    System.out.println("Please enter your choice: ");
                    choice = sc.nextInt();

                    switch (choice) {
                        case 1:
                            System.out.println("How many Students: ");
                            int n = sc.nextInt();

                            for (int i = 0; i < n; i++) {
                                System.out.println("Enter Name: ");
                                String name = sc.next();
                                System.out.println("Enter Id: ");
                                String id = sc.next();
                                System.out.println("Enter Department: ");
                                String dept = sc.next();
                                System.out.println("Enter Cgpa: ");
                                float cgpa = sc.nextFloat();
                                System.out.println("Enter Address: ");
                                String address = sc.next();
                                System.out.println("Enter Age: ");
                                int age = sc.nextInt();
                                System.out.println("Enter ContactNumber: ");
                                long contactNumber = sc.nextLong();

                                A.add(new Student(name, id, dept, cgpa, address, age, contactNumber));
                            }

                            output = new ObjectOutputStream(new FileOutputStream(file));
                            output.writeObject(A);
                            output.close();

                            break;

                        case 2:
                            try {
                                input = new ObjectInputStream(new FileInputStream(file));
                                A = (ArrayList<Student>) input.readObject();
                                input.close();

                                System.out.println("---------------------------------");
                                list = A.listIterator();
                                while (list.hasNext()) {
                                    System.out.println(list.next());
                                }
                                System.out.println("---------------------------------");
                            } catch (IOException | ClassNotFoundException e) {
                                e.printStackTrace();
                            }
                            break;

                        case 3:
                            try {
                                input = new ObjectInputStream(new FileInputStream(file));
                                A = (ArrayList<Student>) input.readObject();
                                input.close();

                                boolean found = false;
                                System.out.println("How many Students: ");
                                int n3 = sc.nextInt();
                                for (int i = 0; i < n3; i++) {
                                    System.out.println("Enter Student's Id To Search:");
                                    String id = sc.next();

                                    System.out.println("-------------------");

                                    list = A.listIterator();
                                    while (list.hasNext()) {
                                        Student S = list.next();

                                        if (S.id.equals(id)) {
                                            System.out.println(S);
                                            found = true;
                                        }
                                    }
                                }
                                if (!found) {
                                    System.out.println("Data not found");
                                }

                                System.out.println("-------------------");
                            } catch (IOException | ClassNotFoundException e) {
                                e.printStackTrace();
                            }
                            break;

                        case 4:
                            try {
                                input = new ObjectInputStream(new FileInputStream(file));
                                A = (ArrayList<Student>) input.readObject();
                                input.close();

                                boolean found = false;
                                System.out.println("How many Students: ");
                                int n1 = sc.nextInt();
                                for (int j = 0; j < n1; j++) {
                                    System.out.println("Enter Student's Id To Delete:");
                                    String id = sc.next();

                                    System.out.println("-------------------");

                                    list = A.listIterator();
                                    while (list.hasNext()) {
                                        Student S = list.next();

                                        if (S.id.equals(id)) {
                                            list.remove();
                                            found = true;
                                        }
                                    }
                                }

                                if (found) {
                                    output = new ObjectOutputStream(new FileOutputStream(file));
                                    output.writeObject(A);
                                    output.close();
                                    System.out.println("Delete Successful");
                                } else {
                                    System.out.println("Data not found");
                                }

                                System.out.println("-------------------");
                            } catch (IOException | ClassNotFoundException e) {
                                e.printStackTrace();
                            }
                            break;

                        case 5:
                            try {
                                input = new ObjectInputStream(new FileInputStream(file));
                                A = (ArrayList<Student>) input.readObject();
                                input.close();

                                boolean found = false;
                                System.out.println("How many Students: ");
                                int n2 = sc.nextInt();
                                for (int k = 0; k < n2; k++) {
                                    System.out.println("Enter Student's Id to Update:");
                                    String id = sc.next();

                                    System.out.println("-------------------");

                                    list = A.listIterator();
                                    while (list.hasNext()) {
                                        Student S = list.next();

                                        if (S.id.equals(id)) {
                                            System.out.println("Enter new Name: ");
                                            String new_name = sc.next();
                                            System.out.println("Enter new Id: ");
                                            String new_id = sc.next();
                                            System.out.println("Enter new Department: ");
                                            String new_dept = sc.next();
                                            System.out.println("Enter new Cgpa: ");
                                            float new_cgpa = sc.nextFloat();
                                            System.out.println("Enter new Address: ");
                                            String new_address = sc.next();
                                            System.out.println("Enter new Age: ");
                                            int new_age = sc.nextInt();
                                            System.out.println("Enter new ContactNumber: ");
                                            long new_contactNumber = sc.nextLong();

                                            list.set(new Student(new_name, new_id, new_dept, new_cgpa, new_address, new_age, new_contactNumber));
                                            found = true;
                                        }
                                    }
                                }

                                if (found) {
                                    output = new ObjectOutputStream(new FileOutputStream(file));
                                    output.writeObject(A);
                                    output.close();

                                    System.out.println("Data Updated Successfully");
                                } else {
                                    System.out.println("Data not found");
                                }

                                System.out.println("-------------------");
                            } catch (IOException | ClassNotFoundException e) {
                                e.printStackTrace();
                            }
                            break;

                        case 0:
                            System.out.println("Exiting the System");
                            System.exit(0);
                            break;

                        default:
                            System.out.println("Wrong choice of Number!!");
                            System.out.println("Try Again!");
                    }
                } while (choice != 0);

                c = 1;
            } else {
                System.out.println("Wrong Information");
                System.out.println("Please ReEnter username and password again!!");
                System.out.print("Enter Username: ");
                user = sc.next();
                System.out.print("Enter password: ");
                pass = sc.nextInt();
            }
        }
    }
}

class Student implements Serializable {
    String name, id, dept, address;
    float cgpa;
    int age;
    long contactNumber;

    public Student(String name, String id, String dept, float cgpa, String address, int age, long contactNumber) {
        this.name = name;
        this.id = id;
        this.dept = dept;
        this.cgpa = cgpa;
        this.address = address;
        this.age = age;
        this.contactNumber = contactNumber;
    }

    @Override
    public String toString() {
        return "Name: " + name + "\nID: " + id + "\nDepartment: " + dept + "\nCGPA: " + cgpa +
                "\nAddress: " + address + "\nAge: " + age + "\nContact Number: " + contactNumber;
    }
}