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Space Character

A space character can be part of a string. A regular expression that describes a set of strings must include any space characters the strings might contain. The regular expression a x describes the set that consists of just one string, a x as above.

The regular expression ax describes the set that consists of just one string, ax without a space.

A string can begin (and can end) with one or several space characters. For example, here is a regular expression that starts with two spaces (this might be hard to see):


The quote marks are not part of the regular expression. They are used here to show the leading spaces. (However, in a Java program, a regular expression is given as a String literal and must be surrounded by quote marks.)

To match a tab character, use \t in the regular expression. To match a newline character, use \n. (These will not work with this chapter's regular expression applet, however.) Chapter 9 shows how to match characters other than the usual alphanumeric ones.


(Review: ) Can an automaton transition be labeled with several characters?