customException.java

public class Main {

    public static void main(String[] args) throws Exception {

        PreCheck preCheck = new PreCheck("4543 5807 9574 0027");
        preCheck.validation();
    }
    
    private static class PreCheck {
        private String _cardNumber;

        public PreCheck(String cardNumber){
            _cardNumber = cardNumber;
        }

        public void validation() throws Exception {
            if(_cardNumber.contains("4543")){
                System.out.println("Login Successful..");
            }
            else{
                throw new Exception("Login Failed..");
            }
        }
    }
}