StudentManager.java

// StudentManager.java
// Handles all file operations and implements StudentsOperations

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

public class StudentManager implements StudentsOperations {

    Scanner sc = new Scanner(System.in); 
    File file = new File("students.txt"); 

    // addStudent() method 
    @Override
    public void addStudent() throws IOException { 
        FileWriter fw = new FileWriter(file, true); 

        System.out.print("Enter Roll No.: ");
        int rollNo = sc.nextInt();
        sc.nextLine(); // consume leftover newline

        System.out.print("Enter Student Name: ");
        String name = sc.nextLine();

        System.out.print("Enter Marks: ");
        double marks = sc.nextDouble();

        String data = rollNo + ", " + name + ", " + marks + "\n";
        fw.write(data);
        fw.close();
        System.out.println("✅ Student Added Successfully!\n");
        System.out.println(data);
    }

    // viewStudents() method
    @Override
    public void viewStudent() throws IOException {
        BufferedReader br = new BufferedReader(new FileReader(file));

        String line;
        System.out.println("\nRoll | Name | Marks");
        System.out.println("-------------------");

        while ((line = br.readLine()) != null) {
            String[] data = line.split(",");
            System.out.println(data[0].trim() + " | " + data[1].trim() + " | " + data[2].trim());
        }

        br.close();
        System.out.println();
    }

    // searchStudent() method
    @Override
    public void searchStudent() throws IOException {
        BufferedReader br = new BufferedReader(new FileReader(file));
        System.out.print("Enter the roll number to search: ");
        int rollNo = sc.nextInt();

        String line;
        boolean found = false;

        while ((line = br.readLine()) != null) {
            String[] data = line.split(",");
            if (Integer.parseInt(data[0].trim()) == rollNo) {
                System.out.println("✅ Found: " + data[1].trim() + " | Marks: " + data[2].trim());
                found = true;
                break;
            }
        }

        if (!found)
            System.out.println("❌ Student not found!");
        br.close();
    }

    // deleteStudent() method
    @Override
    public void deleteStudent() throws IOException {
        System.out.print("Enter Roll No to delete: ");
        int r = sc.nextInt();

        File tempFile = new File("temp.txt");
        BufferedReader br = new BufferedReader(new FileReader(file));
        BufferedWriter bw = new BufferedWriter(new FileWriter(tempFile));

        String line;
        boolean deleted = false;

        while ((line = br.readLine()) != null) {
            String[] data = line.split(",");
            if (Integer.parseInt(data[0].trim()) != r) {
                bw.write(line + "\n");
            } else {
                deleted = true;
            }
        }

        bw.close();
        br.close();
        file.delete();
        tempFile.renameTo(file);

        if (deleted) 
            System.out.println("🗑️ Record deleted successfully!");
        else 
            System.out.println("❌ Roll number not found!");
    }
}