How to add values in arraylist with a switch case in Java

How can I add values or index in arrayList in a switch case?

I have tried without a switch case. It will work well, but in a switch case, it is not working at all! My code run, but I cant add values, for example in case 1.

Here's my code.

import java.util.ArrayList;
import java.util.Scanner;

public class Eqla3tech {

    public static void main(String[] args) {

        menu();
    }

    static void menu() {

        ArrayList<String> cars = new ArrayList<String>();
        Scanner input = new Scanner(System.in);

        System.out.println("Add Student <1>");
        System.out.println("remove Student <2>");
        System.out.println("show list of students <3>");
        System.out.println("how many students? <4>");

        int num = input.nextInt();
        input.nextLine();

        switch(num) {

            case 1:
                System.out.println("write student name!!");

                cars.add(input.next());
                menu();
                break;

            case 2:
                System.out.println("what number of index of student to remove");
                int index = input.nextInt();
                cars.remove(index);
                menu();
                break;

            case 3:
                System.out.println("Here's a list you have added.");
                System.out.println(cars);
                menu();
                break;

            case 4:
                System.out.println("Here's haw many students");
                System.out.println(cars.size());
                menu();
                break;
        }
    }
}

I try to make arrays as dynamic and I can add or remove from switch without losing values.

I have tried to make user enter input, but it did not work. I mean, every time the user enter input, the value is not saved in add arrayList.

I think I am close, but I am lost too.

Your cars list is local to one call of the method called menu().

When you call that method again, it gets a different cars list.

You can solve this by using a loop inside a single call of the menu() method -- such as a do-while loop. Then each pass through the loop will use the same list.