How to avoid System.StringException: No match found when only finding a substring and not a full match?

Question

Preamble

I know (based on this question "No match found" when using Regex in Apex), that I can avoid "No Match Found" by wrapping the results in:

if(pm.matches()){
    //Code
}

However, this appears to be specific to when the Regex is a complete match to the string.

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Scenario

I am trying to find a substring within the string(s), a set of numbers between parenthesis, like this (500). I want to return only the numbers inside the parenthesis, to store this number in a Salesforce number field.

I know I can use pm.find(), but it appears that if it does not find anything, it throws the "No Match Found" error instead of gracefully returning false, meaning I cannot do this:

if(pm.find()){
    // Code
}

The code above would still error when trying to do pm.find on a string with no results found.

ISSUE

I want to be able to put in any string and pull out the number IF one exists, but with this "No Match Found" issue I can't throw a string at it unless that string is guaranteed to have at least one set of numbers inside a parenthesis. Any string that has no numbers will throw the error. I considered putting this in a try{}catch{} block and just catching the errors gracefully, but this doesn't seem like the correct approach.

How can I work around this to be able to check any string but only set the number field in Salesforce in instances where a result is found in the string?

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I've included some execute anonymous code below that shows a success and a failure, for reference:

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SUCCESS

String str = 'Text Messaging Plan (500)';

Pattern p = Pattern.compile('.+\\((\\d+)');
Matcher pm = p.matcher(str);

System.debug('Find? ' + pm.find());
System.debug('PM Group 1: ' + pm.group(1));

---

FAILURE

String str = 'Text Messaging Plan (abc)';

Pattern p = Pattern.compile('.+\\((\\d+)');
Matcher pm = p.matcher(str);

System.debug('Find? ' + pm.find()); // FAILS HERE
System.debug('PM Group 1: ' + pm.group(1));

Answer 1

You're misreading the logs: the error in your "failure" code comes from calling Matcher.group (because there was no match).

Try the following:

String str = 'Text Messaging Plan (abc)';

Pattern p = Pattern.compile('.+\\((\\d+)');
Matcher pm = p.matcher(str);
Boolean found;

System.debug('Find? ' + (found = pm.find())); // (DOES NOT) FAIL HERE
if(found) {
    System.debug('PM Group 1: ' + pm.group(1));
}