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The Java Developers Almanac 1.4Order this book from Amazon. |
e434. Adding Comments to a Regular ExpressionBy default, whitespace in a regular expression is significant. By specifying theCOMMENTS flag, whitespace can be ignored in a pattern.
While in comment mode, a particular whitespace character can be
matched using a character class (for example, [\ ] matches a space).
In comment mode, the It is also possible to enable comments within a pattern using
the inline modifier The inline modifier can also contain pattern characters using
the form CharSequence inputStr = "a b"; String patternStr = "a b"; // Compile without comments Pattern pattern = Pattern.compile(patternStr); Matcher matcher = pattern.matcher(inputStr); boolean matchFound = matcher.matches(); // true // Compile with comments pattern = Pattern.compile(patternStr, Pattern.COMMENTS); matcher = pattern.matcher(inputStr); matchFound = matcher.matches(); // false // Use COMMENTS but include a character class with a space patternStr = "a [\\ ] b"; pattern = Pattern.compile(patternStr, Pattern.COMMENTS); matcher = pattern.matcher(inputStr); matchFound = matcher.matches(); // true // Use an inline modifier matchFound = pattern.matches("a b", inputStr); // true matchFound = pattern.matches("(?x)a b", inputStr); // false matchFound = pattern.matches("(?x)a [\\ ] b", inputStr); // true matchFound = pattern.matches("(?x)a \\s b", inputStr); // true matchFound = pattern.matches("a (?x: b )", inputStr); // true // Tabs and newlines in the pattern are ignored as well matchFound = pattern.matches("(?x)a \t\n \\s b", inputStr); // true // Read pattern from file try { File f = new File("pattern.txt"); FileReader rd = new FileReader(f); char[] buf = new char[(int)f.length()]; rd.read(buf); patternStr = new String(buf); matcher = pattern.matcher(inputStr); matchFound = matcher.matches(); // true } catch (IOException e) { }Here are the contents of pattern.txt: # This pattern matches ``a b'' a # this is the first part [\ ] # this is the second part b # this is the third part
e435. Compiling a Pattern with Multiple Flags
© 2002 Addison-Wesley. |