Validate input option through regular expression pattern in Java

Question

I'm working on Android Java application using regex. I'm trying to validate a sentence like: "I want a xxx pizza" by using a pattern like "I want a (TYPEA|TYPEB|TYPEC) pizza".

An example: I set the pattern to "I want a (salami|mushrooms|cheese) pizza" user inputs: "I want a salami pizza" the sentence is matched correctly and group(1) equals to "salami". But if the user inputs: "I want a capricciosa pizza" the whole matcher fails instead of just the group(1). Can the regex being modified in way to avoid the matcher to fail on the whole sentence and make it just to get a null-group at group(1) position?

Hope my explanation is clear.... thanks in advance.

aioobe · Accepted Answer · 2014-12-23 17:58:29Z

2

Either the entire string is accepted or the entire string is rejected.

If you want a null group if the type of pizza does not match salami|mushrooms|cheese you could do

"I want a (?:(salami|mushrooms|cheese)|(?:.*)) pizza"

(?: ...) is a non-capturing group. And the |(?:.*) would be a "match anything escape hatch" to allow the entire string to be accepted (but still making group(1) null).

Demo:

Pattern p = Pattern.compile("I want a (?:(salami|mushrooms|cheese)|(?:.*)) pizza");

String[] tests = { "I want a salami pizza", "I want a shrimp pizza" };

for (String s : tests) {
    Matcher m = p.matcher(s);
    if (m.matches()) {
        System.out.println(s + ": " + m.group(1));
    }
}

Output:

I want a salami pizza: salami
I want a shrimp pizza: null

edited Dec 23, 2014 at 17:58

answered Dec 23, 2014 at 17:52

aioobe

423k115 gold badges831 silver badges844 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Validate input option through regular expression pattern in Java

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related