JavaFX TextField validation for integer input and also allow either K or k(for Thousand) or M or m(for Million) in last

I want to add validation in javafx TextField such that user should only be able to insert integer values ([0-9] and Dot ). Also user should be able to insert either B or b(for Billion) and K or k (for Thousand) and M or m( for Million). Basically it should be an amountfield. Delete and Backspace should also work.

for example :

10k should become 10,000.00 as soon as user hit k and K should not be displayed on amountfield (textfield) Similarly 10M or 10m should convert into 10,000,000.00

adsadi342fn3 or 31233123werwer or dsad342134k should not be allowed to enter in the textfield.

I have used getKeyChar method while validating TextField in case of Swing. But I need same implementation in case of JavaFx where we don't have getKeyChar method.

I have used the following method but the problem with this is it allows user to enter any value. example : sdafewr23rf

private void amountEntered() {
        if (amountField != null) {
            String value;
            char[] charArray = amountField.getText().toCharArray();
            if (charArray.length > 0)
                switch (charArray[charArray.length - 1]) {
                    case 't':
                    case 'T':
                        value = multiplyValue(amountField.getText(), new BigDecimal(1000000000000.0));
                        updateAmount(value);
                        break;
                    case 'b':
                    case 'B':
                        value = multiplyValue(amountField.getText(), new BigDecimal(1000000000.0));
                        updateAmount(value);
                        break;
                    case 'm':
                    case 'M':
                        value = multiplyValue(amountField.getText(), new BigDecimal(1000000.0));
                        updateAmount(value);
                        break;
                    case 'k':
                    case 'K':
                        value = multiplyValue(amountField.getText(), new BigDecimal(1000.0));
                        updateAmount(value);
                        break;
                    case '0':
                    case '1':
                    case '2':
                    case '3':
                    case '4':
                    case '5':
                    case '6':
                    case '7':
                    case '8':
                    case '9':
                    case '.':
                    case ',':
                        updateAmount(amountField.getText());
                        break;
                    default:
                        break;
                }
        }
    }

private String multiplyValue(String number, BigDecimal multValue) {
        //get rid of "," for double parsing
        BigDecimal value = new BigDecimal(cleanDouble(number.substring(0, number.length() - 1)));
        value = value.multiply(multValue);
        return value.toPlainString();
    }