What is the point of this exercise? To learn REGEX or ... ? I mean we can find the validation code for a phone number online.

Question about the task

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Does anyone have an idea or why this exercise would be useful ? I mean it's not like you have to churn out prep code and think about the logic of the program (unless you want to go the route of if statements like I started). Is it worth trying to remember the regex combinations?

The checkPhoneNumber method should check whether the phoneNumber argument is a valid phone number.

Verification criteria:
1) if the number starts with '+', then it must contain 12 digits
2) if the number starts with a digit or opening parenthesis, then it must contain 10 digits
3) the number may contain 0-2 non-consecutive '-' characters
4) the number may contain 1 pair of matching parentheses, which must be to the left of the '-' characters
5) the parentheses must contain exactly 3 digits
6) the number cannot contain letters
7) the number must end with a digit

Here are some examples:

+380501234567 - true
+38(050)1234567 - true
+38050123-45-67 - true
050123-4567 - true
+38)050(1234567 - false
+38(050)1-23-45-6-7 - false
050xxx4567 - false
050123456 - false
(0)501234567 - false

Requirements:

The checkPhoneNumber method should return a boolean.
The checkPhoneNumber method must be public.
The checkPhoneNumber method must have one String parameter.
The checkPhoneNumber method must correctly check the validity of the phone number passed as an argument.

package com.codegym.task.task22.task2212; /* Phone number verification */ public class Solution { public static boolean checkPhoneNumber(String phoneNumber) { if (phoneNumber == null) return false; /* 3) the number may contain 0-2 non-consecutive '-' characters 4) the number may contain 1 pair of matching parentheses, which must be to the left of the '-' characters 5) the parentheses must contain exactly 3 digits 7) the number must end with a digit 1) if the number starts with '+', then it must contain 12 digits 2) if the number starts with a digit or opening parenthesis, then it must contain 10 digits */ if (phoneNumber.length() < 10) return false; if (phoneNumber.contains("+") && phoneNumber.indexOf("+") > 0) return false; if (phoneNumber.contains("+") && phoneNumber.indexOf("+")==0 && phoneNumber.length() < 12) return false; if (phoneNumber.contains("[a-z]")) return false; if (phoneNumber.substring(phoneNumber.length()-1).equals("[a-z]")) return false; return false; } public static void main(String[] args) { } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

1 April 2021, 16:02

solution

You can google the correct answer to every single one of these tasks. That is not the point though. All of Codegyms tasks are designed to teach you how to think and solve problems, and they are all from real world issues. Personally, with each task, I try to solve it first with my own knowledge. If I am unable to solve it that way then I next start googling only the points that I am stuck on. I have solved 99% of the problems I have faced this way. After solving, and typically struggling, I had a much better understanding of each of the steps algorithmically in solving the greater problem. At that point I would search for better or more succinct ways of solving the problem, typically with techniques I was unfamiliar with (such as regex). It made a lot more sense to me to see the "advanced techniques" and how they are used to solve all those problems that I had to solve on my own. btw... "advanced techniques" is a poor description. All it is is the evolution of design. The first computers were nothing more than some lights and knobs/switches. Someone decided to give them a screen with text. The first inputs were punchards which someone decided a keyboard would be better. Then someone started doing graphics with computers which turned into graphical operating systems, which led to the mouse to navigate, etc etc etc.

Guadalupe Gagnon

Level 37 , Tampa, United States

1 April 2021, 16:13

Some comments on the code that you have already: 1) Make sure that you are counting digits. When it says the number should have 10/12 digits, the .length() method will not return the correct amount of digits: "+12(324)2-1-".length() equals 12 even though it only contains 7 digits 2) make sure you are checking for invalid chars in the phone number string. Checking for [a-z] are only 26 of the possible ~65000 possible invalid chars. *hint* I would check that it only contains the 14 valid chars instead of the invalid ones.

Andrei

Level 41

1 April 2021, 16:15

Obviously you can google the correct answer for each task but that would defeat the purpose of this course. The difference between this exercise and 'regular' ones is that for this exercise there's no algorithm to think about if you don't know your regex (imo) - ok you think of the prepcode (first it should return false is less than 10, or if + is after first char etc but that's as far as you can get without knowing regex; As I said, only if you want to do it with if else statement, then you can devise a more detailed algo but , imo, it would defeat the purpose of regex. So, based on your logic, I should first learn regex to be able to try and solve it with my own knowledge, and then search for methods how they can be tied together. So my question is, is it worth it to spend more time learning the regex cheat sheet at this moment? This is the solution propsed by the mentor:

public static boolean checkPhoneNumber(String telNumber) {
       if (telNumber == null) {
           return false;
       }
       return  (telNumber.matches("^\\+(\\d[\\-()]?){11}\\d$") || telNumber.matches("^[(\\d]-?(\\d[\\-)]?){8}\\d$"))
               && telNumber.matches("^(\\+)?(\\d)*(\\(\\d{3}\\))?(\\d+-?\\d+-?)?\\d+$");
   }