Login Prototype

import java.util.*;


public class LoginPrototype {
    //Arraylist
    private ArrayList<Credentials> allUsers = new ArrayList<Credentials>();

    //Main method to launch the app
    public static void main(String[] args) {
        LoginPrototype main = new LoginPrototype();
        main.displayMainMenu();
    }

    //Display method to view the app
    private void displayMainMenu() {
        int input;
        do {
            //Displaying the Main Menu
            System.out.println("Menu Options");
            System.out.println("[1] Login");
            System.out.println("[2] Register");
            System.out.println("[0] Quit");//5 Displaying Main Menu Options

            //allow Main Menu Input
            Scanner sc = new Scanner(System.in);
            input = sc.nextInt();

           //User Input turned to selection.
            if (input > 2) {
                System.out.println("Only input [0]-[2]");
            } else if (input == 1) {
                System.out.println("Login");
                handleLogin();
            } else if (input == 2) {
                System.out.println("Register");
                register();
            } else if (input == 0) {
                System.out.println("Thanks. Bye");
                break;
            }
        } while (input <= 2);
    }

    private Credentials handleCredentialInput() {
        Scanner sc = new Scanner(System.in);

        String username, password;

        System.out.println("Enter Username: ");
        username = sc.next();
        System.out.println("Enter Password: ");
        password = sc.next();

        Credentials credentials = new Credentials(username, password);

        return credentials;
    }

    //registering the usernames
    private void register() {
        handleCredentialInput();
        if (allUsers.contains(handleCredentialInput())){
            System.out.println("uName Exists");
        }else{
            allUsers.add(handleCredentialInput());
            System.out.println("Successfully added");
        }
    }

    //Method collecting all the users in the arrayList
    private void listUsers(){
        for (Credentials c : allUsers){
            System.out.println(c.getUsername());
        }
    }

    //Handling the Login of the Users
    private void handleLogin() {
        handleCredentialInput();
        if(allUsers.contains(handleCredentialInput())) {
            allUsers.get(allUsers.indexOf(handleCredentialInput()));
            if (handleCredentialInput().getPassword().equals(allUsers.indexOf(handleCredentialInput())))
            System.out.print("Logged In");
        }else {
            System.out.println("Wrong Username or Password");

        }
    }
}