java login

import java.util.ArrayList;
import java.util.Scanner;
import java.io.PrintStream;

class data {
   public static ArrayList<user> usermap = new ArrayList<>();
}
class user {
    public final String username;
    public final String password;
    public user(String u, String p) {
        this.username = u;
        this.password = p;
        data.usermap.add(this);
    }
    public String getPassword() {
        return this.password;
    }
    public String getUsername() {
        return this.username;
    }
}


class Main {
    public static boolean exists(String username) {
        for (int i = 0; i < data.usermap.size(); i++) {
            if (data.usermap.get(i).getUsername().equalsIgnoreCase(username)) {
                return true;
            }
        }
        return false;
    }
    public static user getUser(String username) {
        for (int i = 0; i < data.usermap.size(); i++) {
            if (data.usermap.get(i).getUsername().equalsIgnoreCase(username)) {
                return data.usermap.get(i);
            }
        }
        return null;
    }
    public static int getNextEntryInt() {
        Scanner s = new Scanner(System.in);
        return s.nextInt();
    }
    public static String nextString() {
        Scanner s = new Scanner(System.in);
        return (String) s.next();
    }
    public static void print(String msg) {
        System.out.println(msg);
    }

    PrintStream p = new PrintStream(System.out);
    public static void main(String[] args) {
        program();
    }
    public static void program() {
        String huser;
        String hpass;
        int opt;
        print("Welcome!\n1. Login\n2. Register\n");
        opt = getNextEntryInt();
        if (opt == 1) {
            print("Enter username: ");
            huser = nextString();
            if (exists(huser)) {
                print("Enter password: ");
                hpass = nextString();
                if (getUser(huser).getPassword().equalsIgnoreCase(hpass)) {
                    print("logged in!");
                    program();
                } else {
                    print("invalid password!");
                    program();
                }
            } else {
                print("invalid username!");
                program();
            }




        } else if (opt == 2) {
            String htempuser;
            print("Enter a username: ");
            htempuser = nextString();
            if (!exists(htempuser)) {
              print("enter a password: ");
              new user(htempuser, nextString());
              print("Registered!");
              program();
            } else {
               print("user already Registered!");
               program();
            }
        } else {
            print("invalid args!");
            program();
        }
    }
    }