java.lang.Objectjava.util.regex.Matcher
public final class Matcher
An engine that performs match operations on a character sequence by interpreting a Pattern .
A matcher is created from a pattern by invoking the pattern's matcher method. Once created, a matcher can be used to perform three different kinds of match operations:
The matches method attempts to match the entire input sequence against the pattern.
The lookingAt method attempts to match the input sequence, starting at the beginning, against the pattern.
The find method scans the input sequence looking for the next subsequence that matches the pattern.
Each of these methods returns a boolean indicating success or failure. More information about a successful match can be obtained by querying the state of the matcher.
A matcher finds matches in a subset of its input called the region . By default, the region contains all of the matcher's input. The region can be modified via the region method and queried via the regionStart and regionEnd methods. The way that the region boundaries interact with some pattern constructs can be changed. See useAnchoringBounds and useTransparentBounds for more details.
This class also defines methods for replacing matched subsequences with new strings whose contents can, if desired, be computed from the match result. The appendReplacement and appendTail methods can be used in tandem in order to collect the result into an existing string buffer, or the more convenient replaceAll method can be used to create a string in which every matching subsequence in the input sequence is replaced.
The explicit state of a matcher includes the start and end indices of the most recent successful match. It also includes the start and end indices of the input subsequence captured by each capturing group in the pattern as well as a total count of such subsequences. As a convenience, methods are also provided for returning these captured subsequences in string form.
The explicit state of a matcher is initially undefined; attempting to query any part of it before a successful match will cause an IllegalStateException to be thrown. The explicit state of a matcher is recomputed by every match operation.
The implicit state of a matcher includes the input character sequence as well as the append position , which is initially zero and is updated by the appendReplacement method.
A matcher may be reset explicitly by invoking its reset() method or, if a new input sequence is desired, its reset(CharSequence) method. Resetting a matcher discards its explicit state information and sets the append position to zero.
Instances of this class are not safe for use by multiple concurrent threads.
Method Summary | |
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Matcher |
appendReplacement
(
StringBuffer
sb,
String
replacement) Implements a non-terminal append-and-replace step. |
StringBuffer |
appendTail
(
StringBuffer
sb) Implements a terminal append-and-replace step. |
int |
end
() Returns the offset after the last character matched. |
int |
end
(int group) Returns the offset after the last character of the subsequence captured by the given group during the previous match operation. |
boolean |
find
() Attempts to find the next subsequence of the input sequence that matches the pattern. |
boolean |
find
(int start) Resets this matcher and then attempts to find the next subsequence of the input sequence that matches the pattern, starting at the specified index. |
String |
group
() Returns the input subsequence matched by the previous match. |
String |
group
(int group) Returns the input subsequence captured by the given group during the previous match operation. |
int |
groupCount
() Returns the number of capturing groups in this matcher's pattern. |
boolean |
hasAnchoringBounds
() Queries the anchoring of region bounds for this matcher. |
boolean |
hasTransparentBounds
() Queries the transparency of region bounds for this matcher. |
boolean |
hitEnd
() Returns true if the end of input was hit by the search engine in the last match operation performed by this matcher. |
boolean |
lookingAt
() Attempts to match the input sequence, starting at the beginning of the region, against the pattern. |
boolean |
matches
() Attempts to match the entire region against the pattern. |
Pattern |
pattern
() Returns the pattern that is interpreted by this matcher. |
static String |
quoteReplacement
(
String
s) Returns a literal replacement String for the specified String. |
Matcher |
region
(int start, int end) Sets the limits of this matcher's region. |
int |
regionEnd
() Reports the end index (exclusive) of this matcher's region. |
int |
regionStart
() Reports the start index of this matcher's region. |
String |
replaceAll
(
String
replacement) Replaces every subsequence of the input sequence that matches the pattern with the given replacement string. |
String |
replaceFirst
(
String
replacement) Replaces the first subsequence of the input sequence that matches the pattern with the given replacement string. |
boolean |
requireEnd
() Returns true if more input could change a positive match into a negative one. |
Matcher |
reset
() Resets this matcher. |
Matcher |
reset
(
CharSequence
input) Resets this matcher with a new input sequence. |
int |
start
() Returns the start index of the previous match. |
int |
start
(int group) Returns the start index of the subsequence captured by the given group during the previous match operation. |
MatchResult |
toMatchResult
() Returns the match state of this matcher as a MatchResult . |
String |
toString
() Returns the string representation of this matcher. |
Matcher |
useAnchoringBounds
(boolean b) Sets the anchoring of region bounds for this matcher. |
Matcher |
usePattern
(
Pattern
newPattern) Changes the Pattern that this Matcher uses to find matches with. |
Matcher |
useTransparentBounds
(boolean b) Sets the transparency of region bounds for this matcher. |
Methods inherited from class java.lang. Object |
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clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait |
Method Detail |
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public Pattern pattern()
public MatchResult toMatchResult()
public Matcher usePattern(Pattern newPattern)
This method causes this matcher to lose information about the groups of the last match that occurred. The matcher's position in the input is maintained and its last append position is unaffected.
public Matcher reset()
Resetting a matcher discards all of its explicit state information and sets its append position to zero. The matcher's region is set to the default region, which is its entire character sequence. The anchoring and transparency of this matcher's region boundaries are unaffected.
public Matcher reset(CharSequence input)
Resetting a matcher discards all of its explicit state information and sets its append position to zero. The matcher's region is set to the default region, which is its entire character sequence. The anchoring and transparency of this matcher's region boundaries are unaffected.
public int start()
public int start(int group)
Capturing groups are indexed from left to right, starting at one. Group zero denotes the entire pattern, so the expression m. start(0) is equivalent to m. start() .
public int end()
public int end(int group)
Capturing groups are indexed from left to right, starting at one. Group zero denotes the entire pattern, so the expression m. end(0) is equivalent to m. end() .
public String group()
For a matcher m with input sequence s , the expressions m. group() and s. substring( m. start(), m. end()) are equivalent.
Note that some patterns, for example a* , match the empty string. This method will return the empty string when the pattern successfully matches the empty string in the input.
public String group(int group)
For a matcher m , input sequence s , and group index g , the expressions m. group( g ) and s. substring( m. start( g ), m. end( g )) are equivalent.
Capturing groups are indexed from left to right, starting at one. Group zero denotes the entire pattern, so the expression m.group(0) is equivalent to m.group() .
If the match was successful but the group specified failed to match any part of the input sequence, then null is returned. Note that some groups, for example (a*) , match the empty string. This method will return the empty string when such a group successfully matches the empty string in the input.
public int groupCount()
Group zero denotes the entire pattern by convention. It is not included in this count.
Any non-negative integer smaller than or equal to the value returned by this method is guaranteed to be a valid group index for this matcher.
public boolean matches()
If the match succeeds then more information can be obtained via the start , end , and group methods.
public boolean find()
This method starts at the beginning of this matcher's region, or, if a previous invocation of the method was successful and the matcher has not since been reset, at the first character not matched by the previous match.
If the match succeeds then more information can be obtained via the start , end , and group methods.
public boolean find(int start)
If the match succeeds then more information can be obtained via the start , end , and group methods, and subsequent invocations of the find() method will start at the first character not matched by this match.
public boolean lookingAt()
Like the matches method, this method always starts at the beginning of the region; unlike that method, it does not require that the entire region be matched.
If the match succeeds then more information can be obtained via the start , end , and group methods.
public static String quoteReplacement(String s)
public Matcher appendReplacement(StringBuffer sb, String replacement)
This method performs the following actions:
It reads characters from the input sequence, starting at the append position, and appends them to the given string buffer. It stops after reading the last character preceding the previous match, that is, the character at index start() - 1 .
It appends the given replacement string to the string buffer.
It sets the append position of this matcher to the index of the last character matched, plus one, that is, to end() .
The replacement string may contain references to subsequences captured during the previous match: Each occurrence of $ g will be replaced by the result of evaluating group ( g ) . The first number after the $ is always treated as part of the group reference. Subsequent numbers are incorporated into g if they would form a legal group reference. Only the numerals '0' through '9' are considered as potential components of the group reference. If the second group matched the string "foo" , for example, then passing the replacement string "$2bar" would cause "foobar" to be appended to the string buffer. A dollar sign ( $ ) may be included as a literal in the replacement string by preceding it with a backslash ( \$ ).
Note that backslashes ( \ ) and dollar signs ( $ ) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string. Dollar signs may be treated as references to captured subsequences as described above, and backslashes are used to escape literal characters in the replacement string.
This method is intended to be used in a loop together with the appendTail and find methods. The following code, for example, writes one dog two dogs in the yard to the standard-output stream:
Pattern p = Pattern.compile("cat"); Matcher m = p.matcher("one cat two cats in the yard"); StringBuffer sb = new StringBuffer(); while (m.find()) { m.appendReplacement(sb, "dog"); } m.appendTail(sb); System.out.println(sb.toString());
public StringBuffer appendTail(StringBuffer sb)
This method reads characters from the input sequence, starting at the append position, and appends them to the given string buffer. It is intended to be invoked after one or more invocations of the appendReplacement method in order to copy the remainder of the input sequence.
public String replaceAll(String replacement)
This method first resets this matcher. It then scans the input sequence looking for matches of the pattern. Characters that are not part of any match are appended directly to the result string; each match is replaced in the result by the replacement string. The replacement string may contain references to captured subsequences as in the appendReplacement method.
Note that backslashes ( \ ) and dollar signs ( $ ) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string. Dollar signs may be treated as references to captured subsequences as described above, and backslashes are used to escape literal characters in the replacement string.
Given the regular expression a*b , the input "aabfooaabfooabfoob" , and the replacement string "-" , an invocation of this method on a matcher for that expression would yield the string "-foo-foo-foo-" .
Invoking this method changes this matcher's state. If the matcher is to be used in further matching operations then it should first be reset.
public String replaceFirst(String replacement)
This method first resets this matcher. It then scans the input sequence looking for a match of the pattern. Characters that are not part of the match are appended directly to the result string; the match is replaced in the result by the replacement string. The replacement string may contain references to captured subsequences as in the appendReplacement method.
Note that backslashes ( \ ) and dollar signs ( $ ) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string. Dollar signs may be treated as references to captured subsequences as described above, and backslashes are used to escape literal characters in the replacement string.
Given the regular expression dog , the input "zzzdogzzzdogzzz" , and the replacement string "cat" , an invocation of this method on a matcher for that expression would yield the string "zzzcatzzzdogzzz" .
Invoking this method changes this matcher's state. If the matcher is to be used in further matching operations then it should first be reset.
public Matcher region(int start, int end)
Depending on the transparency and anchoring being used (see useTransparentBounds and useAnchoringBounds ), certain constructs such as anchors may behave differently at or around the boundaries of the region.
public int regionStart()
public int regionEnd()
public boolean hasTransparentBounds()
This method returns true if this matcher uses transparent bounds, false if it uses opaque bounds.
See useTransparentBounds for a description of transparent and opaque bounds.
By default, a matcher uses opaque region boundaries.
public Matcher useTransparentBounds(boolean b)
Invoking this method with an argument of true will set this matcher to use transparent bounds. If the boolean argument is false , then opaque bounds will be used.
Using transparent bounds, the boundaries of this matcher's region are transparent to lookahead, lookbehind, and boundary matching constructs. Those constructs can see beyond the boundaries of the region to see if a match is appropriate.
Using opaque bounds, the boundaries of this matcher's region are opaque to lookahead, lookbehind, and boundary matching constructs that may try to see beyond them. Those constructs cannot look past the boundaries so they will fail to match anything outside of the region.
By default, a matcher uses opaque bounds.
public boolean hasAnchoringBounds()
This method returns true if this matcher uses anchoring bounds, false otherwise.
See useAnchoringBounds for a description of anchoring bounds.
By default, a matcher uses anchoring region boundaries.
public Matcher useAnchoringBounds(boolean b)
Invoking this method with an argument of true will set this matcher to use anchoring bounds. If the boolean argument is false , then non-anchoring bounds will be used.
Using anchoring bounds, the boundaries of this matcher's region match anchors such as ^ and $.
Without anchoring bounds, the boundaries of this matcher's region will not match anchors such as ^ and $.
By default, a matcher uses anchoring region boundaries.
public String toString()
Returns the string representation of this matcher. The string representation of a Matcher contains information that may be useful for debugging. The exact format is unspecified.
public boolean hitEnd()
Returns true if the end of input was hit by the search engine in the last match operation performed by this matcher.
When this method returns true, then it is possible that more input would have changed the result of the last search.
public boolean requireEnd()
Returns true if more input could change a positive match into a negative one.
If this method returns true, and a match was found, then more input could cause the match to be lost. If this method returns false and a match was found, then more input might change the match but the match won't be lost. If a match was not found, then requireEnd has no meaning.