Class StringSearch
SearchIterator
that provides
language-sensitive text searching based on the comparison rules defined
in a RuleBasedCollator
object.
StringSearch ensures that language eccentricity can be
handled, e.g. for the German collator, characters ß and SS will be matched
if case is chosen to be ignored.
See the
"ICU Collation Design Document" for more information.
There are 2 match options for selection:
Let S' be the sub-string of a text string S between the offsets start and
end [start, end].
A pattern string P matches a text string S at the offsets [start, end]
if
option 1. Some canonical equivalent of P matches some canonical equivalent of S' option 2. P matches S' and if P starts or ends with a combining mark, there exists no non-ignorable combining mark before or after S? in S respectively.Option 2. is the default.
This search has APIs similar to that of other text iteration mechanisms
such as the break iterators in BreakIterator
. Using these
APIs, it is easy to scan through text looking for all occurrences of
a given pattern. This search iterator allows changing of direction by
calling a reset()
followed by a SearchIterator.next()
or SearchIterator.previous()
.
Though a direction change can occur without calling reset()
first,
this operation comes with some speed penalty.
Match results in the forward direction will match the result matches in
the backwards direction in the reverse order
SearchIterator
provides APIs to specify the starting position
within the text string to be searched, e.g. setIndex
,
preceding
and following
.
Since the starting position will be set as it is specified, please take note that
there are some danger points at which the search may render incorrect
results:
- In the midst of a substring that requires normalization.
- If the following match is to be found, the position should not be the second character which requires swapping with the preceding character. Vice versa, if the preceding match is to be found, the position to search from should not be the first character which requires swapping with the next character. E.g certain Thai and Lao characters require swapping.
- If a following pattern match is to be found, any position within a contracting sequence except the first will fail. Vice versa if a preceding pattern match is to be found, an invalid starting point would be any character within a contracting sequence except the last.
A BreakIterator
can be used if only matches at logical breaks are desired.
Using a BreakIterator
will only give you results that exactly matches the
boundaries given by the BreakIterator
. For instance the pattern "e" will
not be found in the string "é" if a character break iterator is used.
Options are provided to handle overlapping matches. E.g. In English, overlapping matches produces the result 0 and 2 for the pattern "abab" in the text "ababab", where mutually exclusive matches only produces the result of 0.
Options are also provided to implement "asymmetric search" as described in UTS #10 Unicode Collation Algorithm, specifically the ElementComparisonType values.
Though collator attributes will be taken into consideration while
performing matches, there are no APIs here for setting and getting the
attributes. These attributes can be set by getting the collator
from getCollator()
and using the APIs in RuleBasedCollator
.
Lastly to update StringSearch to the new collator attributes,
reset()
has to be called.
Restriction:
Currently there are no composite characters that consists of a
character with combining class > 0 before a character with combining
class == 0. However, if such a character exists in the future,
StringSearch does not guarantee the results for option 1.
Consult the SearchIterator
documentation for information on
and examples of how to use instances of this class to implement text
searching.
Note, StringSearch is not to be subclassed.
- Author:
- Laura Werner, synwee
- See Also:
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Nested Class Summary
Nested classes/interfaces inherited from class com.ibm.icu.text.SearchIterator
SearchIterator.ElementComparisonType
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Field Summary
Fields inherited from class com.ibm.icu.text.SearchIterator
breakIterator, DONE, matchLength, targetText
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Constructor Summary
ConstructorsConstructorDescriptionStringSearch
(String pattern, String target) Initializes the iterator to use the language-specific rules and break iterator rules defined in the default locale to search for argument pattern in the argument target text.StringSearch
(String pattern, CharacterIterator target, RuleBasedCollator collator) Initializes the iterator to use the language-specific rules defined in the argument collator to search for argument pattern in the argument target text.StringSearch
(String pattern, CharacterIterator target, RuleBasedCollator collator, BreakIterator breakiter) Initializes the iterator to use the language-specific rules defined in the argument collator to search for argument pattern in the argument target text.StringSearch
(String pattern, CharacterIterator target, ULocale locale) Initializes the iterator to use the language-specific rules and break iterator rules defined in the argument locale to search for argument pattern in the argument target text.StringSearch
(String pattern, CharacterIterator target, Locale locale) Initializes the iterator to use the language-specific rules and break iterator rules defined in the argument locale to search for argument pattern in the argument target text. -
Method Summary
Modifier and TypeMethodDescriptionGets theRuleBasedCollator
used for the language rules.int
getIndex()
Return the current index in the text being searched.Returns the pattern for which StringSearch is searching for.protected int
handleNext
(int position) Abstract method which subclasses override to provide the mechanism for finding the next match in the target text.protected int
handlePrevious
(int position) Abstract method which subclasses override to provide the mechanism for finding the previous match in the target text.boolean
Determines whether canonical matches (option 1, as described in the class documentation) is set.void
reset()
Resets the iteration.void
setCanonical
(boolean allowCanonical) Set the canonical match mode.void
setCollator
(RuleBasedCollator collator) Sets theRuleBasedCollator
to be used for language-specific searching.void
setIndex
(int position) Sets the position in the target text at which the next search will start.protected void
Deprecated.This API is ICU internal only.void
setPattern
(String pattern) Set the pattern to search for.void
setTarget
(CharacterIterator text) Set the target text to be searched.Methods inherited from class com.ibm.icu.text.SearchIterator
first, following, getBreakIterator, getElementComparisonType, getMatchedText, getMatchLength, getMatchStart, getTarget, isOverlapping, last, next, preceding, previous, setBreakIterator, setElementComparisonType, setMatchLength, setOverlapping
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Constructor Details
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StringSearch
public StringSearch(String pattern, CharacterIterator target, RuleBasedCollator collator, BreakIterator breakiter) Initializes the iterator to use the language-specific rules defined in the argument collator to search for argument pattern in the argument target text. The argumentbreakiter
is used to define logical matches. See super class documentation for more details on the use of the target text andBreakIterator
.- Parameters:
pattern
- text to look for.target
- target text to search for pattern.collator
-RuleBasedCollator
that defines the language rulesbreakiter
- ABreakIterator
that is used to determine the boundaries of a logical match. This argument can be null.- Throws:
IllegalArgumentException
- thrown when argument target is null, or of length 0- See Also:
-
StringSearch
Initializes the iterator to use the language-specific rules defined in the argument collator to search for argument pattern in the argument target text. NoBreakIterator
s are set to test for logical matches.- Parameters:
pattern
- text to look for.target
- target text to search for pattern.collator
-RuleBasedCollator
that defines the language rules- Throws:
IllegalArgumentException
- thrown when argument target is null, or of length 0- See Also:
-
StringSearch
Initializes the iterator to use the language-specific rules and break iterator rules defined in the argument locale to search for argument pattern in the argument target text.- Parameters:
pattern
- text to look for.target
- target text to search for pattern.locale
- locale to use for language and break iterator rules- Throws:
IllegalArgumentException
- thrown when argument target is null, or of length 0. ClassCastException thrown if the collator for the specified locale is not a RuleBasedCollator.
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StringSearch
Initializes the iterator to use the language-specific rules and break iterator rules defined in the argument locale to search for argument pattern in the argument target text. See super class documentation for more details on the use of the target text andBreakIterator
.- Parameters:
pattern
- text to look for.target
- target text to search for pattern.locale
- locale to use for language and break iterator rules- Throws:
IllegalArgumentException
- thrown when argument target is null, or of length 0. ClassCastException thrown if the collator for the specified locale is not a RuleBasedCollator.- See Also:
-
StringSearch
Initializes the iterator to use the language-specific rules and break iterator rules defined in the default locale to search for argument pattern in the argument target text.- Parameters:
pattern
- text to look for.target
- target text to search for pattern.- Throws:
IllegalArgumentException
- thrown when argument target is null, or of length 0. ClassCastException thrown if the collator for the default locale is not a RuleBasedCollator.
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Method Details
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getCollator
Gets theRuleBasedCollator
used for the language rules.Since StringSearch depends on the returned
RuleBasedCollator
, any changes to theRuleBasedCollator
result should follow with a call to eitherreset()
orsetCollator(RuleBasedCollator)
to ensure the correct search behavior.- Returns:
RuleBasedCollator
used by this StringSearch- See Also:
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setCollator
Sets theRuleBasedCollator
to be used for language-specific searching.The iterator's position will not be changed by this method.
- Parameters:
collator
- to use for this StringSearch- Throws:
IllegalArgumentException
- thrown when collator is null- See Also:
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getPattern
Returns the pattern for which StringSearch is searching for.- Returns:
- the pattern searched for
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setPattern
Set the pattern to search for. The iterator's position will not be changed by this method.- Parameters:
pattern
- for searching- Throws:
IllegalArgumentException
- thrown if pattern is null or of length 0- See Also:
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isCanonical
public boolean isCanonical()Determines whether canonical matches (option 1, as described in the class documentation) is set. See setCanonical(boolean) for more information.- Returns:
- true if canonical matches is set, false otherwise
- See Also:
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setCanonical
public void setCanonical(boolean allowCanonical) Set the canonical match mode. See class documentation for details. The default setting for this property is false.- Parameters:
allowCanonical
- flag indicator if canonical matches are allowed- See Also:
-
setTarget
Set the target text to be searched. Text iteration will then begin at the start of the text string. This method is useful if you want to reuse an iterator to search within a different body of text.- Overrides:
setTarget
in classSearchIterator
- Parameters:
text
- new text iterator to look for match,- See Also:
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getIndex
public int getIndex()Return the current index in the text being searched. If the iteration has gone past the end of the text (or past the beginning for a backwards search),SearchIterator.DONE
is returned.- Specified by:
getIndex
in classSearchIterator
- Returns:
- current index in the text being searched.
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setIndex
public void setIndex(int position) Sets the position in the target text at which the next search will start. This method clears any previous match.
- Overrides:
setIndex
in classSearchIterator
- Parameters:
position
- position from which to start the next search- See Also:
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reset
public void reset()Resets the iteration. Search will begin at the start of the text string if a forward iteration is initiated before a backwards iteration. Otherwise if a backwards iteration is initiated before a forwards iteration, the search will begin at the end of the text string.- Overrides:
reset
in classSearchIterator
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handleNext
protected int handleNext(int position) Abstract method which subclasses override to provide the mechanism for finding the next match in the target text. This allows different subclasses to provide different search algorithms.If a match is found, the implementation should return the index at which the match starts and should call
SearchIterator.setMatchLength(int)
with the number of characters in the target text that make up the match. If no match is found, the method should returnSearchIterator.DONE
.- Specified by:
handleNext
in classSearchIterator
- Parameters:
position
- The index in the target text at which the search should start.- Returns:
- index at which the match starts, else if match is not found
SearchIterator.DONE
is returned - See Also:
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handlePrevious
protected int handlePrevious(int position) Abstract method which subclasses override to provide the mechanism for finding the previous match in the target text. This allows different subclasses to provide different search algorithms.If a match is found, the implementation should return the index at which the match starts and should call
SearchIterator.setMatchLength(int)
with the number of characters in the target text that make up the match. If no match is found, the method should returnSearchIterator.DONE
.- Specified by:
handlePrevious
in classSearchIterator
- Parameters:
position
- The index in the target text at which the search should start.- Returns:
- index at which the match starts, else if match is not found
SearchIterator.DONE
is returned - See Also:
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setMatchNotFound
Deprecated.This API is ICU internal only.- Overrides:
setMatchNotFound
in classSearchIterator
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