Regex: ?: notation (Question mark and colon notation) in java

Regex: ?: notation (Question mark and colon notation) in java

In regular expressions, the ?: notation is used to create a non-capturing group. A non-capturing group is a group within a regular expression that is used for grouping and applying quantifiers but does not create a capture group. Capture groups are portions of the input string that match a pattern and are "captured" for later reference or extraction. Non-capturing groups are used when you want to group elements together but don't need to capture them as separate groups.

In Java, to create a non-capturing group using the ?: notation, you include it within parentheses in your regular expression pattern. Here's an example to illustrate its usage:

import java.util.regex.*; public class NonCapturingGroupExample { public static void main(String[] args) { String text = "The price is $10.99, not $20.99."; // Match and capture prices using capturing groups Pattern patternWithCapture = Pattern.compile("(\\$\\d+\\.\\d{2})"); Matcher matcherWithCapture = patternWithCapture.matcher(text); while (matcherWithCapture.find()) { System.out.println("Captured: " + matcherWithCapture.group(1)); } // Match prices without capturing groups (non-capturing group) Pattern patternWithoutCapture = Pattern.compile("(?:\\$\\d+\\.\\d{2})"); Matcher matcherWithoutCapture = patternWithoutCapture.matcher(text); while (matcherWithoutCapture.find()) { System.out.println("Matched: " + matcherWithoutCapture.group()); } } }

In this example, we have a text containing prices in the format "$xx.xx." We use regular expressions to match and capture these prices, both with and without capturing groups.

  • The pattern "(\\$\\d+\\.\\d{2})" uses capturing groups to capture the prices.
  • The pattern "(?:\\$\\d+\\.\\d{2})" uses a non-capturing group with the ?: notation to match the prices without capturing them.

When you run this code, you'll see that the capturing group version extracts the prices with "Captured," while the non-capturing group version matches the prices without capturing them as separate groups, showing "Matched."

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