Class StringSearch

java.lang.Object

com.ibm.icu.text.SearchIterator

com.ibm.icu.text.StringSearch

public final class StringSearch
extends SearchIterator

StringSearch is a 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:

• SearchIterator
• RuleBasedCollator

Status:

Stable ICU 2.0.

Nested Class Summary

Nested classes/interfaces inherited from class SearchIterator

SearchIterator.ElementComparisonType

Modifier and Type	Class	Description
static enum	SearchIterator.ElementComparisonType	Option to control how collation elements are compared.

Field Summary

Fields inherited from class SearchIterator

breakIterator, DONE, matchLength, targetText

Modifier and Type	Field	Description
protected BreakIterator	breakIterator	The BreakIterator to define the boundaries of a logical match.
static final int	DONE	DONE is returned by previous() and next() after all valid matches have been returned, and by first() and last() if there are no matches at all.
protected int	matchLength	Length of the most current match in target text.
protected CharacterIterator	targetText	Target text for searching.

Constructor Summary

Constructors

Constructor	Description
StringSearch(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 Type	Method	Description
RuleBasedCollator	getCollator()	Gets the RuleBasedCollator used for the language rules.
int	getIndex()	Return the current index in the text being searched.
String	getPattern()	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	isCanonical()	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 the RuleBasedCollator 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	setMatchNotFound()	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 SearchIterator

first, following, getBreakIterator, getElementComparisonType, getMatchedText, getMatchLength, getMatchStart, getTarget, isOverlapping, last, next, preceding, previous, setBreakIterator, setElementComparisonType, setMatchLength, setOverlapping

Modifier and Type	Method	Description
final int	first()	Returns the first index at which the string text matches the search pattern.
final int	following(int position)	Returns the first index equal or greater than position at which the string text matches the search pattern.
BreakIterator	getBreakIterator()	Returns the BreakIterator that is used to restrict the indexes at which matches are detected.
SearchIterator.ElementComparisonType	getElementComparisonType()	Returns the collation element comparison type.
String	getMatchedText()	Returns the text that was matched by the most recent call to SearchIterator.first(), SearchIterator.next(), SearchIterator.previous(), or SearchIterator.last().
int	getMatchLength()	Returns the length of text in the string which matches the search pattern.
int	getMatchStart()	Returns the index to the match in the text string that was searched.
CharacterIterator	getTarget()	Return the string text to be searched.
boolean	isOverlapping()	Return true if the overlapping property has been set.
final int	last()	Returns the last index in the target text at which it matches the search pattern.
int	next()	Returns the index of the next point at which the text matches the search pattern, starting from the current position The iterator is adjusted so that its current index (as returned by SearchIterator.getIndex()) is the match position if one was found.
final int	preceding(int position)	Returns the first index less than position at which the string text matches the search pattern.
int	previous()	Returns the index of the previous point at which the string text matches the search pattern, starting at the current position.
void	setBreakIterator(BreakIterator breakiter)	Set the BreakIterator that will be used to restrict the points at which matches are detected.
void	setElementComparisonType(SearchIterator.ElementComparisonType type)	Sets the collation element comparison type.
protected void	setMatchLength(int length)	Sets the length of the most recent match in the target text.
void	setOverlapping(boolean allowOverlap)	Determines whether overlapping matches are returned.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

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 argument breakiter is used to define logical matches. See super class documentation for more details on the use of the target text and BreakIterator.

Parameters:

pattern - text to look for.

target - target text to search for pattern.

collator - RuleBasedCollator that defines the language rules

breakiter - A BreakIterator 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:

• BreakIterator
• RuleBasedCollator

Status:

Stable ICU 2.0.

StringSearch

public 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. No BreakIterators 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:

• RuleBasedCollator

Status:

Stable ICU 2.0.

StringSearch

public 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.

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.

Status:

Stable ICU 2.0.

StringSearch

public 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. See super class documentation for more details on the use of the target text and BreakIterator.

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:

• BreakIterator
• RuleBasedCollator
• SearchIterator

Status:

Stable ICU 3.2.

StringSearch

public StringSearch(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.

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.

Status:

Stable ICU 2.0.

Method Details

getCollator

public RuleBasedCollator getCollator()

Gets the RuleBasedCollator used for the language rules.

Since StringSearch depends on the returned RuleBasedCollator, any changes to the RuleBasedCollator result should follow with a call to either reset() or setCollator(RuleBasedCollator) to ensure the correct search behavior.

Returns:

RuleBasedCollator used by this StringSearch

See Also:

• RuleBasedCollator
• setCollator(RuleBasedCollator)

Status:

Stable ICU 2.0.

setCollator

public void setCollator(RuleBasedCollator collator)

Sets the RuleBasedCollator 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:

• getCollator()

Status:

Stable ICU 2.0.

getPattern

public String getPattern()

Returns the pattern for which StringSearch is searching for.

Returns:

the pattern searched for

Status:

Stable ICU 2.0.

setPattern

public void setPattern(String pattern)

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:

• getPattern()

Status:

Stable ICU 2.0.

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:

• setCanonical(boolean)

Status:

Stable ICU 2.8.

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:

• isCanonical()

Status:

Stable ICU 2.8.

setTarget

public void setTarget(CharacterIterator text)

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 class SearchIterator

Parameters:

text - new text iterator to look for match,

See Also:

• SearchIterator.getTarget()

Status:

Stable ICU 2.8.

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 class SearchIterator

Returns:

current index in the text being searched.

Status:

Stable ICU 2.8.

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 class SearchIterator

Parameters:

position - position from which to start the next search

See Also:

• SearchIterator.getIndex()

Status:

Stable ICU 2.8.

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 class SearchIterator

Status:

Stable ICU 2.8.

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 return SearchIterator.DONE.

Specified by:

handleNext in class SearchIterator

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:

• SearchIterator.setMatchLength(int)

Status:

Stable ICU 2.8.

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 return SearchIterator.DONE.

Specified by:

handlePrevious in class SearchIterator

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:

• SearchIterator.setMatchLength(int)

Status:

Stable ICU 2.8.

setMatchNotFound

@Deprecated
protected void setMatchNotFound()

Deprecated.

This API is ICU internal only.

Overrides:

setMatchNotFound in class SearchIterator

Status:

Internal. This API is ICU internal only.