rspec/rules/S5994/java/rule.adoc

Possessive quantifiers in Regex patterns like below improve performance by eliminating needless backtracking:

{noformat}

?+ , *+ , {plus}{plus} , {n}+ , {n,}+ , {n,m}+

{noformat}

But because possessive quantifiers do not keep backtracking positions and never give back, the following sub-patterns should not match only similar characters. Otherwise, possessive quantifiers consume all characters that could have matched the following sub-patterns and nothing remains for the following sub-patterns.


== Noncompliant Code Example

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Pattern pattern1 = Pattern.compile("a++abc");       // Noncompliant, the second 'a' never matches
Pattern pattern2 = Pattern.compile("\\d*+[02468]"); // Noncompliant, the sub-pattern "[02468]" never matches
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== Compliant Solution

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Pattern pattern1 = Pattern.compile("aa++bc");            // Compliant, for example it can match "aaaabc"
Pattern pattern2 = Pattern.compile("\\d*+(?<=[02468])"); // Compliant, for example it can match an even number like "1234"
----