In https://docs.oracle.com/javase/tutorial/java/javaOO/localclasses.html

            PhoneNumber(String phoneNumber){
                // numberLength = 7;
                String currentNumber = phoneNumber.replaceAll(
                  regularExpression, "");
                if (currentNumber.length() == numberLength)
                    formattedPhoneNumber = currentNumber;
                else
                    formattedPhoneNumber = null;
            }

numberLength = 7 => // numberLength = 10

Or, better clarify that the code is being changed that correct numbers only have seven digits (the point of this assignment is to demonstrate effectively final variables.