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Android Reference

Pattern

java.util.regex

Class Pattern

java.lang.Object
- java.util.regex.Pattern

All Implemented Interfaces:: Serializable

public final class Pattern
extends Object
implements Serializable

Patterns are compiled regular expressions. In many cases, convenience methods such as String.matches, String.replaceAll and String.split will be preferable, but if you need to do a lot of work with the same regular expression, it may be more efficient to compile it once and reuse it. The Pattern class and its companion, Matcher, also offer more functionality than the small amount exposed by String.

 // String convenience methods:
 boolean sawFailures = s.matches("Failures: \\d+");
 String farewell = s.replaceAll("Hello, (\\S+)", "Goodbye, $1");
 String[] fields = s.split(":");

 // Direct use of Pattern:
 Pattern p = Pattern.compile("Hello, (\\S+)");
 Matcher m = p.matcher(inputString);
 while (m.find()) { // Find each match in turn; String can't do this.
     String name = m.group(1); // Access a submatch group; String can't do this.
 }

Regular expression syntax

Java supports a subset of Perl 5 regular expression syntax. An important gotcha is that Java has no regular expression literals, and uses plain old string literals instead. This means that you need an extra level of escaping. For example, the regular expression \s+ has to be represented as the string "\\s+".

Escape sequences

\	Quote the following metacharacter (so `\.` matches a literal `.`).
\Q	Quote all following metacharacters until `\E`.
\E	Stop quoting metacharacters (started by `\Q`).
\\	A literal backslash.
\uhhhh	The Unicode character U+hhhh (in hex).
\xhh	The Unicode character U+00hh (in hex).
\cx	The ASCII control character ^x (so `\cH` would be ^H, U+0008).
\a	The ASCII bell character (U+0007).
\e	The ASCII ESC character (U+001b).
\f	The ASCII form feed character (U+000c).
\n	The ASCII newline character (U+000a).
\r	The ASCII carriage return character (U+000d).
\t	The ASCII tab character (U+0009).

Character classes

It's possible to construct arbitrary character classes using set operations:

[abc]	Any one of `a`, `b`, or `c`. (Enumeration.)
[a-c]	Any one of `a`, `b`, or `c`. (Range.)
[^abc]	Any character except `a`, `b`, or `c`. (Negation.)
[[a-f][0-9]]	Any character in either range. (Union.)
[[a-z]&&[jkl]]	Any character in both ranges. (Intersection.)

Most of the time, the built-in character classes are more useful:

\d	Any digit character (see note below).
\D	Any non-digit character (see note below).
\s	Any whitespace character (see note below).
\S	Any non-whitespace character (see note below).
\w	Any word character (see note below).
\W	Any non-word character (see note below).
\p{NAME}	Any character in the class with the given NAME.
\P{NAME}	Any character not in the named class.

Note that these built-in classes don't just cover the traditional ASCII range. For example, \w is equivalent to the character class [\p{Ll}\p{Lu}\p{Lt}\p{Lo}\p{Nd}]. For more details see Unicode TR-18, and bear in mind that the set of characters in each class can vary between Unicode releases. If you actually want to match only ASCII characters, specify the explicit characters you want; if you mean 0-9 use [0-9] rather than \d, which would also include Gurmukhi digits and so forth.

There are also a variety of named classes:

Unicode category names, prefixed by Is. For example \p{IsLu} for all uppercase letters.
POSIX class names. These are 'Alnum', 'Alpha', 'ASCII', 'Blank', 'Cntrl', 'Digit', 'Graph', 'Lower', 'Print', 'Punct', 'Upper', 'XDigit'.
Unicode block names, as used by Character.UnicodeBlock.forName(java.lang.String) prefixed by In. For example \p{InHebrew} for all characters in the Hebrew block.
Character method names. These are all non-deprecated methods from Character whose name starts with is, but with the is replaced by java. For example, \p{javaLowerCase}.

Quantifiers

Quantifiers match some number of instances of the preceding regular expression.

*	Zero or more.
?	Zero or one.
+	One or more.
{n}	Exactly n.
{n,}	At least n.
{n,m}	At least n but not more than m.

Quantifiers are "greedy" by default, meaning that they will match the longest possible input sequence. There are also non-greedy quantifiers that match the shortest possible input sequence. They're same as the greedy ones but with a trailing ?:

*?	Zero or more (non-greedy).
??	Zero or one (non-greedy).
+?	One or more (non-greedy).
{n}?	Exactly n (non-greedy).
{n,}?	At least n (non-greedy).
{n,m}?	At least n but not more than m (non-greedy).

Quantifiers allow backtracking by default. There are also possessive quantifiers to prevent backtracking. They're same as the greedy ones but with a trailing +:

*+	Zero or more (possessive).
?+	Zero or one (possessive).
++	One or more (possessive).
{n}+	Exactly n (possessive).
{n,}+	At least n (possessive).
{n,m}+	At least n but not more than m (possessive).

Zero-width assertions

^	At beginning of line.
$	At end of line.
\A	At beginning of input.
\b	At word boundary.
\B	At non-word boundary.
\G	At end of previous match.
\z	At end of input.
\Z	At end of input, or before newline at end.

Look-around assertions

Look-around assertions assert that the subpattern does (positive) or doesn't (negative) match after (look-ahead) or before (look-behind) the current position, without including the matched text in the containing match. The maximum length of possible matches for look-behind patterns must not be unbounded.

(?=a)	Zero-width positive look-ahead.
(?!a)	Zero-width negative look-ahead.
(?<=a)	Zero-width positive look-behind.
(?<!a)	Zero-width negative look-behind.

Groups

(a)	A capturing group.
(?:a)	A non-capturing group.
(?>a)	An independent non-capturing group. (The first match of the subgroup is the only match tried.)
\n	The text already matched by capturing group n.

See Matcher.group(int) for details of how capturing groups are numbered and accessed.

Operators

ab	Expression a followed by expression b.
a\|b	Either expression a or expression b.

Flags

(?dimsux-dimsux:a)	Evaluates the expression a with the given flags enabled/disabled.
(?dimsux-dimsux)	Evaluates the rest of the pattern with the given flags enabled/disabled.

The flags are:

`i`	`CASE_INSENSITIVE`	case insensitive matching
`d`	`UNIX_LINES`	only accept `'\n'` as a line terminator
`m`	`MULTILINE`	allow `^` and `$` to match beginning/end of any line
`s`	`DOTALL`	allow `.` to match `'\n'` ("s" for "single line")
`u`	`UNICODE_CASE`	enable Unicode case folding
`x`	`COMMENTS`	allow whitespace and comments

Either set of flags may be empty. For example, (?i-m) would turn on case-insensitivity and turn off multiline mode, (?i) would just turn on case-insensitivity, and (?-m) would just turn off multiline mode.

Note that on Android, UNICODE_CASE is always on: case-insensitive matching will always be Unicode-aware.

There are two other flags not settable via this mechanism: CANON_EQ and LITERAL. Attempts to use CANON_EQ on Android will throw an exception.

Implementation notes

The regular expression implementation used in Android is provided by ICU. The notation for the regular expressions is mostly a superset of those used in other Java language implementations. This means that existing applications will normally work as expected, but in rare cases Android may accept a regular expression that is not accepted by other implementations.

In some cases, Android will recognize that a regular expression is a simple special case that can be handled more efficiently. This is true of both the convenience methods in String and the methods in Pattern.

See Also:: Matcher, Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`static int`	`CANON_EQ` This constant specifies that a character in a `Pattern` and a character in the input string only match if they are canonically equivalent.
`static int`	`CASE_INSENSITIVE` This constant specifies that a `Pattern` is matched case-insensitively.
`static int`	`COMMENTS` This constant specifies that a `Pattern` may contain whitespace or comments.
`static int`	`DOTALL` This constant specifies that the '.' meta character matches arbitrary characters, including line endings, which is normally not the case.
`static int`	`LITERAL` This constant specifies that the whole `Pattern` is to be taken literally, that is, all meta characters lose their meanings.
`static int`	`MULTILINE` This constant specifies that the meta characters '^' and '$' match only the beginning and end of an input line, respectively.
`static int`	`UNICODE_CASE` This constant specifies that a `Pattern` that uses case-insensitive matching will use Unicode case folding.
`static int`	`UNIX_LINES` This constant specifies that a pattern matches Unix line endings ('\n') only against the '.', '^', and '$' meta characters.

Method Summary

Methods
Modifier and Type	Method and Description
`static Pattern`	`compile(String pattern)` Equivalent to `Pattern.compile(pattern, 0)`.
`static Pattern`	`compile(String regularExpression, int flags)` Returns a compiled form of the given `regularExpression`, as modified by the given `flags`.
`protected void`	`finalize()` Invoked when the garbage collector has detected that this instance is no longer reachable.
`int`	`flags()` Returns the flags supplied to `compile`.
`Matcher`	`matcher(CharSequence input)` Returns a `Matcher` for this pattern applied to the given `input`.
`static boolean`	`matches(String regularExpression, CharSequence input)` Tests whether the given `regularExpression` matches the given `input`.
`String`	`pattern()` Returns the regular expression supplied to `compile`.
`static String`	`quote(String string)` Quotes the given `string` using "\Q" and "\E", so that all meta-characters lose their special meaning.
`String[]`	`split(CharSequence input)` Equivalent to `split(input, 0)`.
`String[]`	`split(CharSequence input, int limit)` Splits the given `input` at occurrences of this pattern.
`String`	`toString()` Returns a string containing a concise, human-readable description of this object.

Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - UNIX_LINES
```
public static final int UNIX_LINES
```
    This constant specifies that a pattern matches Unix line endings ('\n') only against the '.', '^', and '$' meta characters. Corresponds to (?d).
    
    See Also:
    Constant Field Values
  - CASE_INSENSITIVE
```
public static final int CASE_INSENSITIVE
```
    This constant specifies that a Pattern is matched case-insensitively. That is, the patterns "a+" and "A+" would both match the string "aAaAaA". See UNICODE_CASE. Corresponds to (?i).
    
    See Also:
    Constant Field Values
  - COMMENTS
```
public static final int COMMENTS
```
    This constant specifies that a Pattern may contain whitespace or comments. Otherwise comments and whitespace are taken as literal characters. Corresponds to (?x).
    
    See Also:
    Constant Field Values
  - MULTILINE
```
public static final int MULTILINE
```
    This constant specifies that the meta characters '^' and '$' match only the beginning and end of an input line, respectively. Normally, they match the beginning and the end of the complete input. Corresponds to (?m).
    
    See Also:
    Constant Field Values
  - LITERAL
```
public static final int LITERAL
```
    This constant specifies that the whole Pattern is to be taken literally, that is, all meta characters lose their meanings.
    
    See Also:
    Constant Field Values
  - DOTALL
```
public static final int DOTALL
```
    This constant specifies that the '.' meta character matches arbitrary characters, including line endings, which is normally not the case. Corresponds to (?s).
    
    See Also:
    Constant Field Values
  - UNICODE_CASE
```
public static final int UNICODE_CASE
```
    This constant specifies that a Pattern that uses case-insensitive matching will use Unicode case folding. On Android, UNICODE_CASE is always on: case-insensitive matching will always be Unicode-aware. If your code is intended to be portable and uses case-insensitive matching on non-ASCII characters, you should use this flag. Corresponds to (?u).
    
    See Also:
    Constant Field Values
  - CANON_EQ
```
public static final int CANON_EQ
```
    This constant specifies that a character in a Pattern and a character in the input string only match if they are canonically equivalent. It is (currently) not supported in Android.
    
    See Also:
    Constant Field Values
- Method Detail
  - matcher
```
public Matcher matcher(CharSequence input)
```
    Returns a Matcher for this pattern applied to the given input. The Matcher can be used to match the Pattern against the whole input, find occurrences of the Pattern in the input, or replace parts of the input.
  - split
```
public String[] split(CharSequence input,
             int limit)
```
    Splits the given input at occurrences of this pattern.
    If this pattern does not occur in the input, the result is an array containing the input (converted from a CharSequence to a String).
    Otherwise, the limit parameter controls the contents of the returned array as described below.
    Parameters:
    limit - Determines the maximum number of entries in the resulting array, and the treatment of trailing empty strings.
    
    For n > 0, the resulting array contains at most n entries. If this is fewer than the number of matches, the final entry will contain all remaining input.
    For n < 0, the length of the resulting array is exactly the number of occurrences of the Pattern plus one for the text after the final separator. All entries are included.
    For n == 0, the result is as for n < 0, except trailing empty strings will not be returned. (Note that the case where the input is itself an empty string is special, as described above, and the limit parameter does not apply there.)
  - split
```
public String[] split(CharSequence input)
```
    Equivalent to split(input, 0).
  - pattern
```
public String pattern()
```
    Returns the regular expression supplied to compile.
  - toString
```
public String toString()
```
    Description copied from class: Object
    Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression:
```
   getClass().getName() + '@' + Integer.toHexString(hashCode())
```
    See Writing a useful toString method if you intend implementing your own toString method.
    Overrides:
    
    toString in class Object
    
    Returns:
    a printable representation of this object.
  - flags
```
public int flags()
```
    Returns the flags supplied to compile.
  - compile
```
public static Pattern compile(String regularExpression,
              int flags)
                       throws PatternSyntaxException
```
    Returns a compiled form of the given regularExpression, as modified by the given flags. See the flags overview for more on flags.
    
    Throws:
    
    PatternSyntaxException - if the regular expression is syntactically incorrect.
    See Also:
    CANON_EQ, CASE_INSENSITIVE, COMMENTS, DOTALL, LITERAL, MULTILINE, UNICODE_CASE, UNIX_LINES
  - compile
```
public static Pattern compile(String pattern)
```
    Equivalent to Pattern.compile(pattern, 0).
  - matches
```
public static boolean matches(String regularExpression,
              CharSequence input)
```
    Tests whether the given regularExpression matches the given input. Equivalent to Pattern.compile(regularExpression).matcher(input).matches(). If the same regular expression is to be used for multiple operations, it may be more efficient to reuse a compiled Pattern.
    
    See Also:
    compile(java.lang.String, int), Matcher.matches()
  - quote
```
public static String quote(String string)
```
    Quotes the given string using "\Q" and "\E", so that all meta-characters lose their special meaning. This method correctly escapes embedded instances of "\Q" or "\E". If the entire result is to be passed verbatim to compile(java.lang.String, int), it's usually clearer to use the LITERAL flag instead.
  - finalize
```
protected void finalize()
                 throws Throwable
```
    Description copied from class: Object
    
    Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.
    Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.
    If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.
    Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.
    Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.
    
    Overrides:
    
    finalize in class Object
    
    Throws:
    
    Throwable

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IT. Expert System.

Android Reference

Pattern

Class Pattern

Regular expression syntax

Escape sequences

Character classes

Quantifiers

Zero-width assertions

Look-around assertions

Groups

Operators

Flags

Implementation notes

Field Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

UNIX_LINES

CASE_INSENSITIVE

COMMENTS

MULTILINE

LITERAL

DOTALL

UNICODE_CASE

CANON_EQ

Method Detail

matcher

split

split

pattern

toString

flags

compile

compile

matches

quote

finalize

Android Reference

Java basics

Java Enterprise Edition (EE)

Java Standard Edition (SE)

SQL

HTML

PHP

CSS

Java Script

MYSQL

JQUERY

VBS

REGEX

C

C++

C#

Design patterns

RFC (standard status)

RFC (proposed standard status)

RFC (draft standard status)

RFC (informational status)

RFC (experimental status)

RFC (best current practice status)

RFC (historic status)

RFC (unknown status)

IT dictionary