6
06/11/2024 7:21 am
Topic starter
- What is regex and how can I use it in Java (and IntelliJ Idea)?
- Are there site which explains regex's use?
- Can you please share?
Thanks, Jolie
3 Answers
5
06/11/2024 7:22 am
You can use regex in Java with the following Classes: Pattern and Matcher;
Here's an example:
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String line = scanner.nextLine();//GETTING THE INPUT LINE
Pattern pattern = Pattern.compile("\\|(.*?)\\|");
Matcher matcher = pattern.matcher(line);
while (matcher.find()) {
\\SOME LOGIC GOES HERE....
}
}
4
06/11/2024 7:22 am
To generate the regix - you can use these 2 sites:
and
Both sites explain a lot abou the regix and you can easily generate some by comparing the regex and the input text 🙂
For the escaping in regex in Java you might want to use this online tool: http://www.freeformatter.com/java-dotnet-escape.html although, IntelliJ IDEA escapes what is needed by itself 🙂 That is what I call a SMART IDE 🙂
2
06/11/2024 7:24 am
Particularly for Java, I use this link (Oracle's documentation): http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html
Everything is explained nicely there!
You can also use the table below to better understand regex:
Summary of regular-expression constructs:
| Construct: | Matches: |
|---|---|
| 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 |
| \x{h...h} | The character with hexadecimal value 0xh...h (Character.MIN_CODE_POINT <= 0xh...h <= Character.MAX_CODE_POINT) |
| \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] |
| \h | A horizontal whitespace character: [ \t\xA0\u1680\u180e\u2000-\u200a\u202f\u205f\u3000] |
| \H | A non-horizontal whitespace character: [^\h] |
| \s | A whitespace character: [ \t\n\x0B\f\r] |
| \S | A non-whitespace character: [^\s] |
| \v | A vertical whitespace character: [\n\x0B\f\r\x85\u2028\u2029] |
| \V | A non-vertical whitespace character: [^\v] |
| \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}\x20] |
\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] |
| java.lang.Character classes (simple java character type) | |
| \p{javaLowerCase} | Equivalent to java.lang.Character.isLowerCase() |
| \p{javaUpperCase} | Equivalent to java.lang.Character.isUpperCase() |
| \p{javaWhitespace} | Equivalent to java.lang.Character.isWhitespace() |
| \p{javaMirrored} | Equivalent to java.lang.Character.isMirrored() |
| Classes for Unicode scripts, blocks, categories and binary properties | |
\p{IsLatin} |
A Latin script character (script) |
\p{InGreek} |
A character in the Greek block (block) |
\p{Lu} |
An uppercase letter (category) |
\p{IsAlphabetic} |
An alphabetic character (binary property) |
\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 |
| Linebreak matcher | |
| \R | Any Unicode linebreak sequence, is equivalent to \u000D\u000A|[\u000A\u000B\u000C\u000D\u0085\u2028\u2029] |
| 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 |
| \k<name> | Whatever the named-capturing group "name" 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 (named-capturing and non-capturing) | |
| (?<name>X) | X, as a named-capturing group |
| (?:X) | X, as a non-capturing group |
| (?idmsuxU-idmsuxU) | Nothing, but turns match flags i d m s u x U on - off |
| (?idmsux-idmsux:X) | X, as a non-capturing group with the given flags i d m s u x 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 |
The precedence of character-class operators is as follows, from highest to lowest:
| 1 | Literal escape | \x |
|---|---|---|
| 2 | Grouping | [...] |
| 3 | Range | a-z |
| 4 | Union | [a-e][i-u] |
| 5 | Intersection | [a-z&&[aeiou]] |
