Regular expression

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--predefined character class:

Character Matches Character Matches

\d any digit \D any nondigit

\w any word character \W any nonword character

\s any white-space character \S any nonwhite-space

character

Note that in java, we should start the escape sequence \ in a String, the two \ are needed, for example a character class attempting to match any digit one or more times, the subexpression should be \\d+ .

--custom define character class:

[aeiou] matches a SINGLE character in the [], that is a vowel;

-regular expression operator

operator description

* match zero or more occurrences of the subexpression

(quantifier) immediately preceding the "*"

+ match one or more occurrences of the subexpression

immediately preceding the "+"

| matches the expression to its left or to its right, and the

parentheses () are used to group parts of the regex ,

for example "Hi(Bruce|Jane)"

Quantifier                      Matches
*                                        Matches zero or more occurrences of the pattern.
+                                       Matches one or more occurrences of the pattern.
?                                       Matches zero or one occurrences of the pattern.
{n}                                     Matches exactly n occurrences.
{n,}                                    Matches at least n occurrences.
{n,m}                                 Matches between n and m (inclusive) occurrences.

metacharacters supported by Java API are: <([{\^-=$!|]})?*+.>

Miscellaneous

Apostrophe: the mark '

Hyphen: the mark -