StringSearch

public final class StringSearch
extends SearchIterator

java.lang.Object
   ↳ android.icu.text.SearchIterator
     ↳ android.icu.text.StringSearch


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 next() or 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.

Summary

Inherited constants

Inherited fields

Public constructors

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, 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, 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.

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, 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.

Public methods

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.

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.

void setPattern(String pattern)

Set the pattern to search for.

void setTarget(CharacterIterator text)

Set the target text to be searched.

Protected methods

int handleNext(int position)

Abstract method which subclasses override to provide the mechanism for finding the next match in the target text.

int handlePrevious(int position)

Abstract method which subclasses override to provide the mechanism for finding the previous match in the target text.

Inherited methods

Public constructors

StringSearch

added in API level 24
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 String: text to look for.

target CharacterIterator: target text to search for pattern.

collator RuleBasedCollator: RuleBasedCollator that defines the language rules

breakiter BreakIterator: 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

StringSearch

added in API level 24
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 String: text to look for.

target CharacterIterator: target text to search for pattern.

collator RuleBasedCollator: RuleBasedCollator that defines the language rules

Throws
IllegalArgumentException thrown when argument target is null, or of length 0

See also:

StringSearch

added in API level 24
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 String: text to look for.

target CharacterIterator: target text to search for pattern.

locale 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.

StringSearch

added in API level 24
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 String: text to look for.

target CharacterIterator: target text to search for pattern.

locale ULocale: 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.

StringSearch

added in API level 24
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 String: text to look for.

target String: 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.

Public methods

getCollator

added in API level 24
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 RuleBasedCollator used by this StringSearch

getIndex

added in API level 24
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), DONE is returned.

Returns
int current index in the text being searched.

getPattern

added in API level 24
String getPattern ()

Returns the pattern for which StringSearch is searching for.

Returns
String the pattern searched for

isCanonical

added in API level 24
boolean isCanonical ()

Determines whether canonical matches (option 1, as described in the class documentation) is set. See setCanonical(boolean) for more information.

Returns
boolean true if canonical matches is set, false otherwise

reset

added in API level 24
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.

setCanonical

added in API level 24
void setCanonical (boolean allowCanonical)

Set the canonical match mode. See class documentation for details. The default setting for this property is false.

Parameters
allowCanonical boolean: flag indicator if canonical matches are allowed

See also:

setCollator

added in API level 24
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 RuleBasedCollator: to use for this StringSearch

Throws
IllegalArgumentException thrown when collator is null

See also:

setIndex

added in API level 24
void setIndex (int position)

Sets the position in the target text at which the next search will start. This method clears any previous match.

Parameters
position int: position from which to start the next search

setPattern

added in API level 24
void setPattern (String pattern)

Set the pattern to search for. The iterator's position will not be changed by this method.

Parameters
pattern String: for searching

Throws
IllegalArgumentException thrown if pattern is null or of length 0

See also:

setTarget

added in API level 24
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.

Parameters
text CharacterIterator: new text iterator to look for match,

Protected methods

handleNext

added in API level 24
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 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 DONE.

Parameters
position int: The index in the target text at which the search should start.

Returns
int index at which the match starts, else if match is not found DONE is returned

handlePrevious

added in API level 24
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 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 DONE.

Parameters
position int: The index in the target text at which the search should start.

Returns
int index at which the match starts, else if match is not found DONE is returned