How to Validate a String with Colon Restriction

Question

I am trying to write a boolean function to support double colons :: only for a string. It should reject any string with non-consecutive colon or more than two consecutive colons. The appearance of double colons can be any number. I can write regex which supports double colons but I don't know how to reject so many combinations of non-consecutive and consecutivec colons. Any idea is appreciated!

Valid inputs: Customer::Table, Customer::Table::Sub

Invalid inputs: Customer:Table, Customer::Table:Sub, Customer::::Table

Can you give example of valid and invalid input please ? – thibsc Apr 20 '20 at 23:34 — thibsc, Apr 20 '20 at 23:34
@thibsc update the description with few examples. – dashenswen Apr 20 '20 at 23:38 — dashenswen, Apr 20 '20 at 23:38

Tim Biegeleisen · Accepted Answer · 2020-04-21T00:06:26.207

3

Here is one line option using String#matches:

String input = "Customer::Table::Sub";
if (input.matches("[^:]+(?:::[^:]+)*")) {
    System.out.println("MATCH");
}

Demo

Here is an explanation of the regex used:

[^:]+          match one or more non colon characters
(?:            start non capturing group
    ::[^:]+    match :: again followed by one or more non :
)*             the group occurring zero or more times

edited Apr 21 '20 at 00:06

answered Apr 20 '20 at 23:34

Tim Biegeleisen

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Elegant! I tried few other combinations and they all worked. Can you add some explanation around ```(?:::[^:]+)``` ? – dashenswen Apr 21 '20 at 00:00
I have added an explanation to the regex. – Tim Biegeleisen Apr 21 '20 at 00:06
Thanks. I wonder if we really need the non-capturing group? Seems the purpose of it is to parse the string but my function will be a boolean function. – dashenswen Apr 21 '20 at 00:10
@dashenswen You may remove the non capturing group, but leaving it in might boost performance slightly. – Tim Biegeleisen Apr 21 '20 at 00:15
Can you shoot me a quick link with the explanation that why it might boost performance – dashenswen Apr 21 '20 at 00:18
Read: [What is a non-capturing group in regular expressions?](https://stackoverflow.com/questions/3512471/what-is-a-non-capturing-group-in-regular-expressions) – Tim Biegeleisen Apr 21 '20 at 00:23

How to Validate a String with Colon Restriction

1 Answers1

Demo