ArrayList goes wrong

The purpose of this function is to find some students that match the ID which I entered in the console. Instead of adding some student to the list at first, I try to Update/Delete student using their ID, and then the if-statement runs, not the else- statement. Is the arraylist I passed to the function is empty at first ?

This is the function

public void updateAndDelete(ArrayList<Student> listStudent) {
        String choice;
        String idKey;
        ArrayList<Student> keyStudent = new ArrayList<Student>();

        // Add students to display
        System.out.print("Enter student's ID to find: ");
        idKey = sc.nextLine().trim();
        for (int i = 0; i < listStudent.size(); i++) {
            if (listStudent.get(i).getId().equals(idKey)) {
                keyStudent.add(listStudent.get(i));
            } 
            if (keyStudent.isEmpty()) {
                System.out.println("No student matches!");
                return;
            }
        }
        display(keyStudent);

        // Update - Delete
        do {
            System.out.println("Do you want to update (U) or delete (D) ?");
            choice = sc.nextLine().trim();
            if (choice.toUpperCase().equals("U")) {
                for (int i = 0; i < listStudent.size(); i++) {
                    if (listStudent.get(i).getId().equals(idKey)) {
                        System.out.print("Update student name: ");
                        listStudent.get(i).setName(sc.nextLine().trim());
                        System.out.print("Update student address: ");
                        listStudent.get(i).setAddress(sc.nextLine().trim());
                        if (listStudent.get(i) instanceof IT) {
                            // Validate Java score
                            String input;
                            do {
                                System.out.print("Update Java score: ");
                                input = sc.nextLine().trim();
                                if (!input.matches(dv.scorePattern)) {
                                    System.out.println("Wrong input!");
                                }
                            } while (!input.matches(dv.scorePattern));
                            ((IT) listStudent.get(i)).setJavaScore(Double.valueOf(input));
                            // Validate CSS score
                            do {
                                System.out.print("Update CSS score: ");
                                input = sc.nextLine().trim();
                                if (!input.matches(dv.scorePattern)) {
                                    System.out.println("Wrong input!");
                                }
                            } while (!input.matches(dv.scorePattern));
                            ((IT) listStudent.get(i)).setCssScore(Double.valueOf(input));
                        }
                        if (listStudent.get(i) instanceof Biz) {
                            String input;
                            // Validate Accounting score
                            do {
                                System.out.print("Enter Accounting score: ");
                                input = sc.nextLine().trim();
                                if (!input.matches(dv.scorePattern)) {
                                    System.out.println("Wrong input!");
                                }
                            } while (!input.matches(dv.scorePattern));
                            ((Biz) listStudent.get(i)).setAccScore(Double.valueOf(input));
                            // Validate Marketing score
                            do {
                                System.out.print("Enter Marketing score: ");
                                input = sc.nextLine().trim();
                                if (!input.matches(dv.scorePattern)) {
                                    System.out.println("Wrong input!");
                                }
                            } while (!input.matches(dv.scorePattern));
                            ((Biz) listStudent.get(i)).setMarScore(Double.valueOf(input));
                        }
                    }
                }
                System.out.println("Student updated!");
                return;
            } else if (choice.toUpperCase().equals("D")) {
                for (int i = 0; i < listStudent.size(); i++) {
                    if (listStudent.get(i).getId().equals(idKey)) {
                        listStudent.remove(i);
                    }
                }
                System.out.println("Student removed!");
                return;
            } else {
                System.out.println("Wrong input!");
            }
        } while (!(choice.equals("U") || choice.equals("D")));

    }

This is display function:

public void display(ArrayList<Student> listStudent) {
        // Alignment
        String alignment = "| %-8s | %-20s | %-12s | %-5.1f | %-5.1f | %-5.1f | %-5.1f | %-5.1f |%n";
        System.out
                .format("+----------+----------------------+--------------+-------+-------+-------+-------+-------+%n");
        System.out
                .format("| ID       | Name                 | Address      | Java  | CSS   | Acc.  | Mar.  | GPA   |%n");
        System.out
                .format("+----------+----------------------+--------------+-------+-------+-------+-------+-------+%n");
        // Loop
        for (int i = 0; i < listStudent.size(); i++) {
            if (listStudent.get(i) instanceof IT) {
                System.out.format(alignment, listStudent.get(i).getId(), listStudent.get(i).getName(),
                        listStudent.get(i).getAddress(), ((IT) listStudent.get(i)).getJavaScore(),
                        ((IT) listStudent.get(i)).getCssScore(), null, null, ((IT) listStudent.get(i)).avgScore());
            }
            if (listStudent.get(i) instanceof Biz) {
                System.out.format(alignment, listStudent.get(i).getId(), listStudent.get(i).getName(),
                        listStudent.get(i).getAddress(), null, null, ((Biz) listStudent.get(i)).getAccScore(),
                        ((Biz) listStudent.get(i)).getMarScore(), ((Biz) listStudent.get(i)).avgScore());
            }
        }
        System.out
                .format("+----------+----------------------+--------------+-------+-------+-------+-------+-------+%n");
    }

Thanks for your help!