Element Insertion & Deletion in a Vector

/*Write a menu-driven progroam to insert and delete various objects in a vector of the specified size.*/
import java.util.Vector;
import java.util.Scanner;
class Employee{
    int id;
}
class Student{
    int roll_no;
}
class Practice{
    public static void main(String[] args){
        Vector v = new Vector(20);
        Scanner sc = new Scanner(System.in);
        while(true){
            System.out.print("\nThe vector is ");
            if(v.size() == 0) System.out.print("Empty!");
            else for(int i = 0; i< v.size(); i++)
                    System.out.print(" " + v.elementAt(i)+ " ");
            System.out.println("\n\n1. Insert 2. Delete 3. Exit");
            int choice = sc.nextInt();
            switch(choice){
                case 1: System.out.println("Insert a 1. Integer 2. Double 3. Float 4. String 5. Array of Strings 6. Employee Object 7. Student Object.");
                    int type = sc.nextInt();
                    switch(type){
                        case 1: System.out.print("Enter the integer: ");
                            v.addElement(new Integer(sc.nextInt())); break;
                        case 2: System.out.print("Enter the double: ");
                        v.addElement(new Double(sc.nextDouble())); break;
                        case 3: System.out.print("Enter the float: ");
                            v.addElement(new Float(sc.nextFloat())); break;
                        case 4: System.out.print("Enter the String: ");
                            v.addElement(sc.next()); break;
                        case 5: System.out.print("Enter no. of strings: ");
                            String[] string = new String[sc.nextInt()];
                            for(String i : string) i = sc.next();
                            for(String i : string) v.addElement(i); break;
                        case 6: System.out.print("Enter the ID of employee: ");
                            Employee em = new Employee();
                            v.addElement(em.id = sc.nextInt()); break;
                        case 7: System.out.print("Enter the roll no: ");
                            Student st = new Student();
                            v.addElement(st.roll_no = sc.nextInt()); break;
                        default:System.out.println("Invalid choice!");
                        } break;
                case 2: System.out.println("Enter the element's index: ");
                    v.removeElementAt(sc.nextInt()); break;
                case 3: return;
                default: System.out.println("Wrong Choice!");
            }
        }
    }
}