Common symbols to represent Regex pattern in java

Regular expressions helping symbols

Let X and Z be 2 regex to be searched.

Symbol	Description
.X	Matches any character
^X	regex must match at the beginning of the line
X$	Finds regex must match at the end of the line
[abc]	Set definition, can match the letter a or b or c. Note that it matches only 1 character.
[^abc]	When a "^" appears as the first character inside [] when it negates the pattern. This can match any character except a or b or c
[abc[vz]]	Set definition, can match a or b or c followed by either v or z
[a-d]	Ranges between a and d…a,b,c,d. Its kind of inclusive range, where it includes a and d as well.
[a-d1-3]	Ranges between a and d…a,b,c,d and numbers in range of 1-4, ie. 1,2,3,4
X|Z	Finds X or Z
XZ	Finds X directly followed by Z
$	Checks if a line end follows

Common predefined patterns

\d	any digit
\D	any non digit
\w	any word character
\W	any non-word character
\s	any white space
\S	any non white space
\S+	Several non-white space character

 

Quantifiers

Symbol	Description	Example
*	Occurs zero or more times, is short for {0,}	X* - Finds no or several letter X, .* - any character sequence
+	Occurs one or more times, is short for {1,}	X+ - Finds one or several letter X
?	Occurs no or one times, ? is short for {0,1}	X? -Finds no or exactly one letter X
{X}	Occurs X number of times, {} describes the order of the preceding liberal	\d{3} - Three digits, .{10} - any character sequence of length 10
{X,Y}	.Occurs between X and Y times,	\d{1,4}- \d must occur at least once and at a maximum of four
*?	? after a qualifier makes it a "reluctant quantifier", it tries to find the smallest match.

 

Note:

The backslash is an escape character in Java Strings. e.g. backslash has a predefine meaning in Java. You have to use "\\" to define a single backslash. If you want to define "\w" then you must be using "\\w" in your regex. If you want to use backslash you as a literal you have to type \\\\ as \ is also a escape charactor in regular expressions.