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Regular expressions simplify pattern-matching code

Discover the elegance of regular expressions in text-processing scenarios that involve pattern matching

By Jeff Friesen, JavaWorld.com, 02/07/03

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Page 13 of 16

one caterpillar, two caterpillars, or three caterpillars on a fence


Two other text replacement methods make it possible to replace either the first match or all matches with replacement text:

  • public String replaceFirst(String replacement): resets the matcher, creates a new String object, copies all the matcher's text characters (up to the first match) to String, appends the replacement characters to String, copies remaining characters to String, and returns that object's reference. (The replacement string may contain references to text sequences captured during the previous match, via dollar-sign characters and capturing group numbers.)
  • public String replaceAll(String replacement): operates similarly to the previous method. However, replaceAll(String replacement) replaces all matches with replacement's characters.


The \s+ regex detects one or more occurrences of whitespace characters in text. The following example uses that regex and calls the replaceAll(String replacement) method to remove duplicate whitespace from text: 

Pattern p = Pattern.compile ("\\s+");
Matcher m = p.matcher ("Remove     the \t\t duplicate whitespace.   ");
System.out.println (m.replaceAll (" "));


The example produces the following output:

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