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Tutorial Part 3
Pattern Elements
\A, \Z, ^, $, \b, \B
There pattern elements "^" and "\A" matches the beginning of a String.
Regex r = new Regex("^.....");
r.search("Hello world.");
System.out.println(r.stringMatched());
// Prints "Hello"
r.search(" Hello world.");
System.out.println(r.didMatch());
// Prints "false"
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Likewise, the pattern element "$" or "\Z" matches the end of
a String.
Regex r = new Regex(".......$");
r.search("Say goodbye");
System.out.println(r.stringMatched());
// Prints "goodbye"
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You may, however, be interested in matching on a
different sort of boundary, a "word boundary." This
is the sort of thing you search for when you select
a "match whole word" option from a search dialog
box in a word processor. For example, suppose you
wish to match on the word "some" but not words like
"somehow" or "twosome."
Regex r = new Regex("\\bsome\\b");
r.search("somehow");
System.out.println(""+r.didMatch());
// Prints "false"
r.search("twosome");
System.out.println(""+r.didMatch());
// Prints "false"
r.search("some");
System.out.println(""+r.didMatch());
// Prints "true"
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The "\\b" pattern element matches on the space
between a word character ("\\w" or "[a-zA-Z0-9_]")
or a non-word character ("\\W" or "[^a-zA-Z0-9_]").
It will also match on the beginning or end of a
String.
There is also a "\\B" that will fail to match on a
boundary that is a word boundary. In this example
we want to match on a word that begins with the word
word "some" but does not include the word "some."
Regex r = new Regex("\\bsome\\B");
r.search("somehow");
System.out.println(""+r.didMatch());
// Prints "true"
r.search("twosome");
System.out.println(""+r.didMatch());
// Prints "false"
r.search("some");
System.out.println(""+r.didMatch());
// Prints "false"
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