StudentData.java

import java.util.Scanner;
import java.util.HashMap;

class Student {
    public String name;
    public int rollno;
    public int age;
    public int marks;
   

    public Student(String name, int rollno, int age, int marks) { // constructor funct.
        this.name = name;
        this.rollno = rollno;
        this.age = age;
        this.marks = marks;
    }
    

    public  void ViewStudent() { 
        System.out.println("Name:" + name);
        System.out.println("Rollno:" + rollno);
        System.out.println("Age:" + age);
        System.out.println("Marks:" + marks);
    }
}

public class StudentData {

public static void main(String[] args) {
        try{
        Scanner sc = new Scanner(System.in); 

        HashMap<Integer, Student> database = new HashMap<>();

        while (true) { 
            System.out.println(" 1.  Add  student");
            System.out.println(" 2.  View student");
            System.out.println(" 3.  Search  student");
            System.out.println(" 4.  CAlculate avg marks");
            System.out.println(" 5.  Exit");
            System.out.print("Enter your Choice :");
            int choice = sc.nextInt();
             sc.nextLine(); 
            switch (choice) {
                case 1:
                    System.out.print("Enter your name:");
                    String name = sc.nextLine();
                    System.out.print("Enter your roll number :");
                    int rollno = sc.nextInt();
                    System.out.print("Enter your age :");
                    int age = sc.nextInt();
                    System.out.print("Enter your marks :");
                    int marks = sc.nextInt();
                    Student std = new Student(name, rollno, age, marks);
                    database.put(rollno, std); 
                    System.out.println("Student added successfully");
                    break;
                case 2:
                    System.out.println("List of Students:");
                    for (Student i : database.values()) {
                        i.ViewStudent(); 
                    }
                    break;
                case 3:
                    System.out.println("Enter your rollno.");
                    int roll = sc.nextInt();
                  
                    Student data = database.get(roll);
                    if (data != null) { 
                        data.ViewStudent();
                    } else {
                        System.out.println("Student not found");
                    }
                    System.out.println("*************************************************");
                    break;
                case 4:
                    int totalStudents = database.size();
                    int totalMarks = 0;
                    for (Student j : database.values()) {
                        totalMarks = totalMarks + j.marks;
                        double average = (double) totalMarks / totalStudents;
                        System.out.println("Average Marks:" + average);
                    }
                    break;
                case 5:
                    System.exit(0); 
                    break;
                default:
                    System.out.println("Invaild Choice :");
                    break;
            }
        }
  
    }
    catch(Exception e){
        System.out.println(e.getMessage());
    }
}

}