ENCODING {encodingType}
@author stefano.bertini[at]gmail.com
Character classes may appear within other character classes, and may be composed by the union operator (implicit) and the intersection operator (&&). The union operator denotes a class that contains every character that is in at least one of its operand classes. The intersection operator denotes a class that contains every character that is in both of its operand classes.
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]]
Note that a different set of metacharacters are in effect inside a character class than outside a character class. For instance, the regular expression . loses its special meaning inside a character class, while the expression - becomes a range forming metacharacter. A line terminator is a one- or two-character sequence that marks the end of a line of the input character sequence. The following are recognized as line terminators: If {@link #UNIX_LINES} mode is activated, then the only line terminatorsrecognized are newline characters. The regular expression . matches any character except a line terminator unless the {@link #DOTALL} flag is specified. By default, the regular expressions ^ and $ ignore line terminators and only match at the beginning and the end, respectively, of the entire input sequence. If {@link #MULTILINE} mode is activated then^ matches at the beginning of input and after any line terminator except at the end of input. When in {@link #MULTILINE} mode $matches just before a line terminator or the end of the input sequence. Capturing groups are numbered by counting their opening parentheses from left to right. In the expression ((A)(B(C))), for example, there are four such groups: Group zero always stands for the entire expression. Capturing groups are so named because, during a match, each subsequence of the input sequence that matches such a group is saved. The captured subsequence may be used later in the expression, via a back reference, and may also be retrieved from the matcher once the match operation is complete. The captured input associated with a group is always the subsequence that the group most recently matched. If a group is evaluated a second time because of quantification then its previously-captured value, if any, will be retained if the second evaluation fails. Matching the string "aba" against the expression (a(b)?)+, for example, leaves group two set to "b". All captured input is discarded at the beginning of each match. Groups beginning with (? are pure, non-capturing groups that do not capture text and do not count towards the group total. This class is in conformance with Level 1 of Unicode Technical Standard #18: Unicode Regular Expression Guidelines, plus RL2.1 Canonical Equivalents. Unicode escape sequences such as \u2014 in Java source code are processed as described in \u00A73.3 of the Java Language Specification. Such escape sequences are also implemented directly by the regular-expression parser so that Unicode escapes can be used in expressions that are read from files or from the keyboard. Thus the strings "\u2014" and "\\u2014", while not equal, compile into the same pattern, which matches the character with hexadecimal value 0x2014. Unicode blocks and categories are written with the \p and \P constructs as in Perl. \p{prop} matches if the input has the property prop, while \P{prop} does not match if the input has that property. Blocks are specified with the prefix In, as in InMongolian. Categories may be specified with the optional prefix Is: Both \p{L} and \p{IsL} denote the category of Unicode letters. Blocks and categories can be used both inside and outside of a character class. The supported categories are those of The Unicode Standard in the version specified by the {@link java.lang.Character Character} class. The category names are thosedefined in the Standard, both normative and informative. The block names supported by Categories that behave like the java.lang.Character boolean ismethodname methods (except for the deprecated ones) are available through the same \p{prop} syntax where the specified property has the name javamethodname. The Perl constructs not supported by this class: The conditional constructs (?{X}) and (?(condition)X|Y), The embedded code constructs (?{code}) and (??{code}), The embedded comment syntax (?#comment), and The preprocessing operations \l \u, \L, and \U. Constructs supported by this class but not by Perl: Possessive quantifiers, which greedily match as much as they can and do not back off, even when doing so would allow the overall match to succeed. Character-class union and intersection as described above. Notable differences from Perl: In Perl, \1 through \9 are always interpreted as back references; a backslash-escaped number greater than 9 is treated as a back reference if at least that many subexpressions exist, otherwise it is interpreted, if possible, as an octal escape. In this class octal escapes must always begin with a zero. In this class, \1 through \9 are always interpreted as back references, and a larger number is accepted as a back reference if at least that many subexpressions exist at that point in the regular expression, otherwise the parser will drop digits until the number is smaller or equal to the existing number of groups or it is one digit. Perl uses the g flag to request a match that resumes where the last match left off. This functionality is provided implicitly by the {@link Matcher} class: Repeated invocations of the {@link Matcher#find find} method will resume where the last match left off,unless the matcher is reset. In Perl, embedded flags at the top level of an expression affect the whole expression. In this class, embedded flags always take effect at the point at which they appear, whether they are at the top level or within a group; in the latter case, flags are restored at the end of the group just as in Perl. Perl is forgiving about malformed matching constructs, as in the expression *a, as well as dangling brackets, as in the expression abc], and treats them as literals. This class also accepts dangling brackets but is strict about dangling metacharacters like +, ? and *, and will throw a {@link PatternSyntaxException} if it encounters them. For a more precise description of the behavior of regular expression constructs, please see Mastering Regular Expressions, 3nd Edition, Jeffrey E. F. Friedl, O'Reilly and Associates, 2006. Line terminators
Groups and capturing
1 ((A)(B(C))) 2 (A) 3 (B(C)) 4 (C) Unicode support
Pattern are the valid block names accepted and defined by {@link java.lang.Character.UnicodeBlock#forName(String) UnicodeBlock.forName}. Comparison to Perl 5
Pattern engine performs traditional NFA-based matching with ordered alternation as occurs in Perl 5.
The integer representation of each terminal must be positive. The integer representation of each nonterminal must be negative. @author Lane Schwartz @version $LastChangedDate:2008-09-18 12:47:23 -0500 (Thu, 18 Sep 2008) $
myExpr against a text myString one should first create a Pattern object:Pattern p=new Pattern(myExpr);then obtain a Matcher object:
Matcher matcher=p.matcher(myText);The latter is an automaton that actually performs a search. It provides the following methods:
Flags
Flags (see REFlags interface) change the meaning of some regular expression elements at compiletime. These flags may be passed both as string(see Pattern(String,String)) and as bitwise OR of:
Multithreading
Pattern instances are thread-safe, i.e. the same Pattern object may be used by any number of threads simultaniously. On the other hand, the Matcher objects are NOT thread safe, so, given a Pattern instance, each thread must obtain and use its own Matcher.
@see REFlags
@see Matcher
@see Matcher#setTarget(java.lang.String)
@see Matcher#setTarget(java.lang.String,int,int)
@see Matcher#setTarget(char[],int,int)
@see Matcher#setTarget(java.io.Reader,int)
@see MatchResult
@see MatchResult#group(int)
@see MatchResult#start(int)
@see MatchResult#end(int)
@see MatchResult#length(int)
@see MatchResult#charAt(int,int)
@see MatchResult#prefix()
@see MatchResult#suffix()
There are the following guarantees for coordinates of the points of any pattern:
Each implementation of this interface must fulfil both restriction. The point sets, satisfying these requirements, are called allowed points sets for patterns. Any attempt to create a pattern, the set of points of which is not allowed, leads to {@link TooLargePatternCoordinatesException}.
Note: though patterns are sets of real points, their coordinates are restricted by long-type constant {@link #MAX_COORDINATE}.
Also note: uniform-grid patterns must fulfil, in addition, two similar restrictions for their grid indexes. See more details in the comments to {@link UniformGridPattern} interface,the section "Grid index restrictions".
Below are two important theorems, following from these two restrictions.
Theorem I. If you round the coordinates of all points of a pattern, i.e. replace each pattern's point
The proof of this is complex enough. The paper (in Russian) contains such proof: see the theorem of rounding and the theorem of subtraction in this paper.
It means that you can freely use {@link #round()} method for any pattern:it always constructs another allowed pattern, both in terms of this interface and in terms in {@link UniformGridPattern}, and cannot throw {@link TooLargePatternCoordinatesException}.
Theorem II. If all points of a pattern are integer, i.e. for all pattern's points
Proof.
First of all, let's remind that the computer difference a⊖b, according IEEE 754 standard and Java language specification, is the nearest double value to the precise mathematical difference a−b. Because all pattern's points are integer, the restriction 2 allows to state that any difference xj−Xj can be represented precisely by double type (see the comments to {@link #MAX_COORDINATE} constant).So, we have
Now the proof is simple. If is enough to show that the restrictions will be satisfied for the coordinate index j. The restriction 2 is obvious: (mathematical) subtracting Xj does not change the (mathematical!) differences |xj1−xj2|. The new value of this coordinate for each point will be xj−Xj, where both (x0,x1,...,xn−1) and (X0,X1,...,Xn−1) are some points of the pattern; according the condition 2, this difference lies in range − {@link #MAX_COORDINATE}≤xj−Xj≤ {@link #MAX_COORDINATE}. In other words, the restriction 1 is also satisfied. This completes the proof.
Note: this proof is really correct only for patterns, consisting of integer points only. The reason is that all integer coordinates, fulfilling the restriction 1, and all their differences xj−Xj are represented precisely by double Java type. If a pattern contains non-integer points, the statement of this theorem is not true. For example, for 1-dimensional pattern, consisting of three points x1=2251799813685248.00 (= {@link #MAX_COORDINATE}/2), x2=−2251799813685248.00 (=− {@link #MAX_COORDINATE}/2) and x3=−2251799813685247.75 (=− {@link #MAX_COORDINATE}/2+0.25), subtracting the point x3 by Java “−” operator leads to the pattern x'1=4503599627370496.00 (= {@link #MAX_COORDINATE}) (computer subtraction of double values leads to rounding here), x'2=−0.25 and x'3=0.0, which obviously violates the mathematically precise restriction 2: |x'1−x'2|> {@link #MAX_COORDINATE}.
As a result, there is an obvious conclusion. If p is one of the {@link #points() points} ofsome integer pattern (see above), then the method pattern. {@link #shift(Point) shift}(p. {@link Point#symmetric() symmetric()}) always works successfully and never throw {@link TooLargePatternCoordinatesException}.
The classes, implementing this interface, are immutable and thread-safe: there are no ways to modify settings of the created instance.
AlgART Laboratory 2007–2014
@author Daniel Alievsky @version 1.2 @since JDK 1.5 Pattern defines the behaviour for pattern in the XSLT processing model.
Please note that neither the {@link java.util.regex.Pattern#compile(String)} method nor{@link Matcher} instances are supported. For the later, consider using {@link Pattern#match(String)}.
@author George GeorgovassilisPattern defines the behaviour for pattern in the XSLT processing model.
Please note that neither the {@link java.util.regex.Pattern#compile(String)} method nor{@link Matcher} instances are supported. For the later, consider using {@link Pattern#match(String)}.
@author George GeorgovassilisPlease note that neither the {@link java.util.regex.Pattern#compile(String)} method nor{@link Matcher} instances are supported. For the later, consider using {@link Pattern#match(String)}.
@author George GeorgovassilismyExpr against a text myString one should first create a Pattern object:Pattern p=new Pattern(myExpr);then obtain a Matcher object:
Matcher matcher=p.matcher(myText);The latter is an automaton that actually performs a search. It provides the following methods:
Flags
Flags (see REFlags interface) change the meaning of some regular expression elements at compiletime. These flags may be passed both as string(see Pattern(String,String)) and as bitwise OR of:
Multithreading
Pattern instances are thread-safe, i.e. the same Pattern object may be used by any number of threads simultaniously. On the other hand, the Matcher objects are NOT thread safe, so, given a Pattern instance, each thread must obtain and use its own Matcher.
@see REFlags
@see Matcher
@see Matcher#setTarget(java.lang.String)
@see Matcher#setTarget(java.lang.String,int,int)
@see Matcher#setTarget(char[],int,int)
@see Matcher#setTarget(java.io.Reader,int)
@see MatchResult
@see MatchResult#group(int)
@see MatchResult#start(int)
@see MatchResult#end(int)
@see MatchResult#length(int)
@see MatchResult#charAt(int,int)
@see MatchResult#prefix()
@see MatchResult#suffix()
Please note that neither the {@link java.util.regex.Pattern#compile(String)} method nor{@link Matcher} instances are supported. For the later, consider using {@link Pattern#match(String)}.
@author George Georgovassilis | |
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