Regular expression number

Question

My target is to format next number 01122222222 to this 011-22-22-22-22 First three numbers of number, dash and all next numbers with dash after second one. Already tried:

private String phoneFormat(String phoneNumber){
    String regex = "\\B(?=(\\d{3})+(?!\\d))";
    String formattedPhone = phoneNumber.replaceAll(regex, Constants.Characters.DASH);
    return formattedPhone;
}

but it produce different result.

Answer 1

A regex will do the trick. Replace sets of 2 digits with "-[digit][digit]" as long as you have 3 digits before those.

public static void main(String[] args) {
    String s = "01122222222";
    System.out.println(s.replaceAll("(?<=\\d{3})(\\d{2})+?", "-$1"));
}

Live Example

O/P :

011-22-22-22-22

PS : This approach should NOT be used in prod environment and has been written solely to please my own stubbornness that this problem can be solved using one regex.

Answer 2

Since at first your question wasn't clear, I had a solution for both Java and Javascript. I'll leave the javascript one in here as well just 'cause :-)

Java 8

First we use substring(0,3) to get the first three numbers. We add - to this, and with the remaining group ( x.substring(3) ), we split them in groups of two, and we join them together with String.join and use - as the concatenating character.

String test = "01122222222";
String res = test.substring(0,3) + "-";
String[] parts = test.substring(3).split("(?=(?:..)*$)");
res += String.join("-",parts);

System.out.println(res);

Live Example

---

Pre Java 8

From the comments it became clear that you are not using Java 8, so pre-java8 there are various other solutions. You could use a loop like I have done, and add the last part manually. (Alternatively, you could just create the string with each element in the loop, and take the substring again to remove the last - ).

String test = "01122222222";
String res = test.substring(0,3) + "-";
String[] parts = test.substring(3).split("(?=(?:..)*$)");
for(int i = 0; i < parts.length-1; i++){
    res += parts[i]+"-";
}
res+=parts[parts.length-1];
System.out.println(res);

Live Example

---

Javascript

Using the same logic, you could do this in javascript as well. You can run the snippet to see that the result is actually what you expected.

 var x = "01122222222"; var res = x.substring(0,3) +"-"+ x.substring(3).split(/(?=(?:..)*$)/).join("-"); console.log(res)