public static void main(String[] args) { ArrayList<Human> myArr = new ArrayList<Human>(); Scanner scan = new Scanner(System.in); while (true) { showMenu(); int choice; i = new Scanner(System.in); choice = i.nextInt(); switch (choice) { case 0: System.out.println("Do you want to exit ? (Y/N)"); String ex = scan.nextLine(); if (ex.equals("Y") || ex.equals("y")) { i.close(); scan.close(); System.exit(0); } break; case 1: System.out.println("Please enter the student name :"); String a = scan.nextLine(); System.out.println("Please enter the student age :"); String b = scan.nextLine(); System.out.println("Please enter the student city :"); String c = scan.nextLine(); System.out.println("Please enter the student id :"); String d = scan.nextLine(); System.out.println("Please enter the courses grades :"); String e = scan.nextLine(); Double doubleE = Double.valueOf(e); Student y = new Student(a, b, c, d, doubleE); myArr.add(y); System.out.println("Student added successfully."); break; case 2: System.out.println("Please enter the instructor name :"); String aa = scan.nextLine(); System.out.println("Please enter the instructor age :"); String bb = scan.nextLine(); System.out.println("Please enter the instructor city :"); String cc = scan.nextLine(); System.out.println("Please enter the instructor courses :"); String dd = scan.nextLine(); System.out.println("Please enter the salary :"); String ee = scan.nextLine(); Double doubleEE = Double.valueOf(ee); Instructor x = new Instructor(aa, bb, cc, dd, doubleEE); myArr.add(x); System.out.println("Instructor added successfully."); break; case 3: System.out.println("Please enter the student id :"); String searchString = scan.nextLine(); for (Iterator<Human> it = myArr.iterator(); it.hasNext(); ) { Student z = (Student) it.next(); if ((z.getId().equals(searchString))) { if (z instanceof Student) { it.remove(); System.out.println("Student removed successfully."); break; } } } break; case 4: System.out.println("Please enter the instructors name :"); String searchStringI = scan.nextLine(); for (Iterator<Human> it = myArr.iterator(); it.hasNext(); ) { Human zz = (Human) it.next(); if (zz.getName().equals(searchStringI)) { if (zz instanceof Instructor) { it.remove(); System.out.println("Instructor removed successfully."); break; } } } break; case 5: System.out.println(""); System.out.println("**List of Students**"); for (Human q : myArr) { if (q instanceof Student) { System.out.println(q); } } break; case 6: System.out.println(""); System.out.println("**List of Instructors**"); for (Human qq : myArr) { if (qq instanceof Instructor) { System.out.println(qq); } } break; case 7: System.out.println(""); System.out.println("**List of All University People**"); for (Human qqq : myArr) { System.out.println(qqq); } break; } if (choice != 0) continue; } }