Java Doc for StringSearch.java in  » Internationalization-Localization » icu4j » com » ibm » icu » text » Java Source Code / Java DocumentationJava Source Code and Java Documentation

StringSearch is the concrete subclass of SearchIterator that provides language-sensitive text searching based on the comparison rules defined in a RuleBasedCollator object.

StringSearch uses a version of the fast Boyer-Moore search algorithm that has been adapted to work with the large character set of Unicode. Refer to "Efficient Text Searching in Java", published in the Java Report on February, 1999, for further information on the algorithm.

Users are also strongly encouraged to read the section on String Search and Collation in the user guide before attempting to use this class.

String searching gets alittle complicated when accents are encountered at match boundaries. If a match is found and it has preceding or trailing accents not part of the match, the result returned will include the preceding accents up to the first base character, if the pattern searched for starts an accent. Likewise, if the pattern ends with an accent, all trailing accents up to the first base character will be included in the result.

For example, if a match is found in target text "a\u0325\u0300" for the pattern "a\u0325", the result returned by StringSearch will be the index 0 and length 3 <0, 3>. If a match is found in the target "a\u0325\u0300" for the pattern "\u0300", then the result will be index 1 and length 2 <1, 2>.

In the case where the decomposition mode is on for the RuleBasedCollator, all matches that starts or ends with an accent will have its results include preceding or following accents respectively. For example, if pattern "a" is looked for in the target text "á\u0325", the result will be index 0 and length 2 <0, 2>.

The StringSearch class provides two options to handle accent matching described below:

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, length>
if

 
 option 1. P matches some canonical equivalent string of S'. Suppose the 
 RuleBasedCollator used for searching has a collation strength of 
 TERTIARY, all accents are non-ignorable. If the pattern 
 "a\u0300" is searched in the target text 
 "a\u0325\u0300", 
 a match will be found, since the target text is canonically 
 equivalent to "a\u0300\u0325"
 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. Following the example above, the pattern 
 "a\u0300" will not find a match in "a\u0325\u0300", 
 since
 there exists a non-ignorable accent '\u0325' in the middle of 
 'a' and '\u0300'. Even with a target text of 
 "a\u0300\u0325" a match will not be found because of the 
 non-ignorable trailing accent \u0325.
 

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 dangerous positions which the search may render incorrect results:

• The midst of a substring that requires decomposition.
• If the following match is to be found, the position should not be the second character which requires to be swapped with the preceding character. Vice versa, if the preceding match is to be found, position to search from should not be the first character which requires to be swapped 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, a invalid starting point would be any character within a contracting sequence except the last.

Though collator attributes will be taken into consideration while performing matches, there are no APIs provided in StringSearch for setting and getting the attributes. These attributes can be set by getting the collator from getCollator and using the APIs in com.ibm.icu.text.Collator. To update StringSearch to the new collator attributes, reset() or setCollator(RuleBasedCollator) has to be called.

Consult the String Search user guide and the SearchIterator documentation for more information and examples of use.

This class is not subclassable

Gets the RuleBasedCollator used for the language rules.

Concrete method to provide the mechanism for finding the next forwards match in the target text. See super class documentation for its use.

Concrete method to provide the mechanism for finding the next backwards match in the target text. See super class documentation for its use.

Resets the search iteration.

Set the canonical match mode.

Sets the RuleBasedCollator to be used for language-specific searching.

Sets the position in the target text which the next search will start from to the argument.

Set the pattern to search for.

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 StringSearch.reset() or StringSearch.setCollator(RuleBasedCollator) to ensure the correct search behaviour.

Concrete method to provide the mechanism for finding the next forwards match in the target text. See super class documentation for its use.

Concrete method to provide the mechanism for finding the next backwards match in the target text. See super class documentation for its use.

Resets the search iteration. All properties will be reset to the default value.

Search will begin at the start of the target text 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 target text.

Canonical match option will be reset to false, ie an exact match.

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

Sets the RuleBasedCollator to be used for language-specific searching.

This method causes internal data such as Boyer-Moore shift tables to be recalculated, but the iterator's position is unchanged.

Sets the position in the target text which the next search will start from to the argument. This method clears all previous states.

This method takes the argument position and sets the position in the target text accordingly, without checking if position is pointing to a valid starting point to begin searching.

Search positions that may render incorrect results are highlighted in the class documentation.

Set the pattern to search for.

This method causes internal data such as Boyer-Moore shift tables to be recalculated, but the iterator's position is unchanged.