Regex with ? for a set of words

Question

I want to have a regex for NAME;NAME;NAME and also for NAME;NAME;NAME;NAME where the fourth occurrence of NAME is optional.

I have one regex as (.+);(.+);(.+) which matched the first pattern but not the second. I tried playing with ? but its not working out with (.+);(.+);(.+)(;(.+))? Basically, I want to achieve the fourth (.+) as zero or one occurence.

Answer 1

Using .+ matches 1+ times any character including ;

If you want to match 3 or 4 groups separated by a ; and not including it, you could use a negated character class [^;]+ with an optional group at the end of the pattern.

^([^;]+);([^;]+);([^;]+)(?:;([^;]+))?$

• ^ Start of string
• ([^;]+);([^;]+);([^;]+) Capture group 1, 2 and 3 matching any char except ;
• (?: Non capture group
  • ;([^;]+) Match ; and capture any char except ; in group 4
• )? Close group and make it optional
• $ End of string

Regex demo

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If the parts in between can not contain ; you could also use split and count the number of the parts.

String arr[] = { "NAME;NAME;", "NAME;NAME;NAME", "NAME;NAME;NAME;NAME", "NAME;NAME;NAME;NAME;NAME" };

for (String s  : arr) {
    String [] parts = s.split(";");
    if (parts.length == 3 || parts.length == 4) {
        System.out.println(s);
    }
}

Output

NAME;NAME;NAME
NAME;NAME;NAME;NAME