Many operations can be performed on a "String" using the combination of regular expressions
pattern class of the Java Util package and the String's replace all functionality.
String myString = inputText.replaceAll("\\s+","");
Please note that if we call the replaceAll function on the inputText the String inputText as such is not disturbed. This is because String is immutable class, ie invoking the functions contained in a String does not affect the value contained in the String.
Below are the quick list of useful escape sequence of the regular expression.
\w = Anything that is a word character
\W = Anything that isn't a word character (including punctuation etc)
\s = Anything that is a space character (including space, tab characters etc)
\S = Anything that isn't a space character (including both letters and numbers, as well as punctuation etc)
Other useful regex are given below.
Characters
x
The character x
\\
The backslash character
\0n
The character with octal value 0n (0 <= n <= 7)
\0nn
The character with octal value 0nn (0 <= n <= 7)
\0mnn
The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh
The character with hexadecimal value 0xhh
\uhhhh
The character with hexadecimal value 0xhhhh
\t
The tab character ('\u0009')
\n
The newline (line feed) character ('\u000A')
\r
The carriage-return character ('\u000D')
\f
The form-feed character ('\u000C')
\a
The alert (bell) character ('\u0007')
\e
The escape character ('\u001B')
\cx
The control character corresponding to x
Character classes
[abc]
a, b, or c (simple class)
[^abc]
Any character except a, b, or c (negation)
[a-zA-Z]
a through z or A through Z, inclusive (range)
[a-d[m-p]]
a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]
d, e, or f (intersection)
[a-z&&[^bc]]
a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]
a through z, and not m through p: [a-lq-z](subtraction)
Predefined character classes
.
Any character (may or may not match line terminators)
\d
A digit: [0-9]
\D
A non-digit: [^0-9]
\s
A whitespace character: [ \t\n\x0B\f\r]
\S
A non-whitespace character: [^\s]
\w
A word character: [a-zA-Z_0-9]
\W
A non-word character: [^\w]
POSIX character classes (US-ASCII only)
\p{Lower}
A lower-case alphabetic character: [a-z]
\p{Upper}
An upper-case alphabetic character:[A-Z]
\p{ASCII}
All ASCII:[\x00-\x7F]
\p{Alpha}
An alphabetic character:[\p{Lower}\p{Upper}]
\p{Digit}
A decimal digit: [0-9]
\p{Alnum}
An alphanumeric character:[\p{Alpha}\p{Digit}]
\p{Punct}
Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
\p{Graph}
A visible character: [\p{Alnum}\p{Punct}]
\p{Print}
A printable character: [\p{Graph}]
\p{Blank}
A space or a tab: [ \t]
\p{Cntrl}
A control character: [\x00-\x1F\x7F]
\p{XDigit}
A hexadecimal digit: [0-9a-fA-F]
\p{Space}
A whitespace character: [ \t\n\x0B\f\r]
Classes for Unicode blocks and categories
\p{InGreek}
A character in the Greek block (simple block)
\p{Lu}
An uppercase letter (simple category)
\p{Sc}
A currency symbol
\P{InGreek}
Any character except one in the Greek block (negation)
[\p{L}&&[^\p{Lu}]]
Any letter except an uppercase letter (subtraction)
Boundary matchers
^
The beginning of a line
$
The end of a line
\b
A word boundary
\B
A non-word boundary
\A
The beginning of the input
\G
The end of the previous match
\Z
The end of the input but for the final terminator, if any
\z
The end of the input
Greedy quantifiers
X?
X, once or not at all
X*
X, zero or more times
X+
X, one or more times
X{n}
X, exactly n times
X{n,}
X, at least n times
X{n,m}
X, at least n but not more than m times
Reluctant quantifiers
X??
X, once or not at all
X*?
X, zero or more times
X+?
X, one or more times
X{n}?
X, exactly n times
X{n,}?
X, at least n times
X{n,m}?
X, at least n but not more than m times
Possessive quantifiers
X?+
X, once or not at all
X*+
X, zero or more times
X++
X, one or more times
X{n}+
X, exactly n times
X{n,}+
X, at least n times
X{n,m}+
X, at least n but not more than m times
Logical operators
XY
X followed by Y
X|Y
Either X or Y
(X)
X, as a capturing group
Back references
\n
Whatever the nth capturing group matched
Quotation
\
Nothing, but quotes the following character
\Q
Nothing, but quotes all characters until \E
\E
Nothing, but ends quoting started by \Q
Special constructs (non-capturing)
(?:X)
X, as a non-capturing group
(?idmsux-idmsux)
Nothing, but turns match flags on - off
(?idmsux-idmsux:X)
X, as a non-capturing group with the given flags on - off
(?=X)
X, via zero-width positive lookahead
(?!X)
X, via zero-width negative lookahead
(?<=X)
X, via zero-width positive lookbehind
(?<!X)
X, via zero-width negative lookbehind
(?>X)
X, as an independent, non-capturing group
