![]() ![]() This terminology and semantics easily confuse many beginners. Unfortunately, when we deal with objects we are really dealing with object-handles called references which are passed-by-value as well. If you want to look at all the special characters that can be used in regular expressions in a single table, see the following: Special characters in regular expressions.Java is always pass-by-value. ![]() Indicate numbers of characters or expressions to match. Backreferences refer to a previously captured group in the same regular expression. Groups group multiple patterns as a whole, and capturing groups provide extra submatch information when using a regular expression pattern to match against a string. For example, distinguishing between letters and digits. Character classesĭistinguish different types of characters. AssertionsĪssertions include boundaries, which indicate the beginnings and endings of lines and words, and other patterns indicating in some way that a match is possible (including look-ahead, look-behind, and conditional expressions). The following pages provide lists of the different special characters that fit into each category, along with descriptions and examples. In the string "cbbabbbbcdebc", this pattern will match the substring "abbbbc". When the search for a match requires something more than a direct match, such as finding one or more b's, or finding white space, you can include special characters in the pattern.įor example, to match a single "a" followed by zero or more "b"s followed by "c", you'd use the pattern /ab*c/: the * after "b" means "0 or more occurrences of the preceding item."
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