My "Error" Handler in a While Loop Java doesn't read

Question

My code is working, but the problem is that the error handler, the if statement doesn't read. when the user inputted that does not in the choices of Y/N, for example 'g'.

Enter expression: a+b

Try Again? (Y/N) : g

Enter expression:

_

I WANT TO BE THE RESULT IS:

Enter expression: a+b

Try Again? (Y/N) : g

Error, Please Try Again!

Try Again? (Y/N) :

_

My error handler doesn't read

    if (choice.equals("1")) {
                String YN ="Y";
                while (!YN.equalsIgnoreCase("N")) {
                    System.out.print('\u000C');
                    System.out.print("Enter the Infix Expression: ");
                    String exp = BReader.readLine();
                    try {
                        System.out.println("Postfix Expression: " + infixToPostfix(exp));
                    } catch(Exception e) {
                        System.out.println("Enter correct expression.");
                    }
                    System.out.println();
                    System.out.println("Try Again? (Y/N) : ");
                    YN = BReader.readLine();
                    if(!YN.equalsIgnoreCase("N") || !YN.equalsIgnoreCase("Y")){
                    System.out.print("Error, Please Try Again!");
                    }else{
                    }
                }

Answer 1

You need to loop until you get the right answer, as below. Also, it should be a && join:

        while(!YN.equalsIgnoreCase("N") && !YN.equalsIgnoreCase("Y")){
           System.out.println("Error, Please Try Again!");
           System.out.println("Try Again? (Y/N) : ");
           YN = br.readLine();
        }