Telephone number category using regex pattern

Question

I want to get user input for telephone numbers. I have 2 number categories Golden and Normal. When the user enter certain pattern of a telephone number, the system will automatically determine it as Golden or Normal. I'm having problem to code certain pattern. One of the Golden Pattern number is like this: AB001234 where AB is number like 12,23,34,45,56,67,78 and 89. Here what I got so far.

    public static void main(String[] args) {

    Scanner userinput = new Scanner(System.in);


    System.out.println("Enter Telephone Number");
    String nophone = userinput.next();

    String Golden = "(\\d)(\\1)002345|(\\d*)12345$";
    //I want to add AB001234 pattern to the line above but I don't know how.


    if (nophone.matches(Golden)) {
        System.out.println("Golden");
    }


    else {
        System.out.println("Normal");
    }
    }

I'm not sure do I really have to use regex or not. One more question, you can see the first part of String Golden is without $ while the second part has $. I'm not sure the effect if I put or remove the $ symbol.

Answer 1

(\\\\d)(\\\\1) does not check for the sequence like 12 , 23 and so on.. Rather it checks for two smae consecutive digits like 11 , 22 , 33 , ...

To check for sequence, you would have to do it explicitly using Pipe(|) - (12|23|34|45|...)

So, your pattern for Golden Number should be like this: -

^(?:12|23|34|45|56|67|78|89)001234$

(?:..) - Means a non-capturing group . It will not be captured as a numbered group in your pattern.

NOTE: - If the length of your sequence is varying, then Regex is not an appropriate way to match them.

For your second question, $ denotes the end of the string. So, the pattern with $ at the end, will be matched at the end of the string. Also, Caret (^) is there to match the beginning of the string.

For eg: -

• abc$ matches the string "asdfabc" , but not "sdfabcf" .
• ^abc matches the string "abcfsdf" , but not "sdfabcf" .
• ^abc$ only matches the string "abc" , because it is the only string, that starts and ends with "abc" .

You can go through the following links to learn more about Regexp : -

• http://docs.oracle.com/javase/tutorial/essential/regex/
• http://docs.oracle.com/javase/tutorial/essential/regex/quant.html
• http://www.vogella.com/articles/JavaRegularExpressions/article.html

Answer 2

To get this:

AB001234 where AB is number like 12,23,34,45,56,67,78 and 89. Here what I got so far

The regex would look like:

^(12|23|34|45|56|67|78|89)001234$

The $ symbol means end of the string. This means that if there is any aditional character after the last one, the string won't match the Regex.

The ^ symbol means the begining of the string.

For further information, please, check the Summary of regular-expression constructs at the Javadoc API.