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Java 9 Regular Expressions by Anubhava Srivastava

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Eager matching

At this point, it is important to understand one important behavior of regular expression engines, called eagerness. A regular expression engine performs a match operation from left to right in an input string. While matching a regex pattern against the input string, the regex engine moves from left to right and is always eager to complete a match, even though there are other alternative ways in the regular expression to complete the match. Once a substring is matched, it stops proceeding further and returns the match. Only when a character position fails to match all the possible permutations of the regular expression, then the regex engine moves character by character to attempt a match at the next position in the input string. ...

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