com.ibm.icu.text

Class SearchIterator

Known Direct Subclasses:
StringSearch

public abstract class SearchIterator
extends Object

SearchIterator is an abstract base class that defines a protocol for text searching. Subclasses provide concrete implementations of various search algorithms. A concrete subclass, StringSearch, is provided that implements language-sensitive pattern matching based on the comparison rules defined in a RuleBasedCollator object. Instances of SearchIterator maintain a current position and scan over the target text, returning the indices where a match is found and the length of each match. Generally, the sequence of forward matches will be equivalent to the sequence of backward matches.One case where this statement may not hold is when non-overlapping mode is set on and there are continuous repetitive patterns in the text. Consider the case searching for pattern "aba" in the text "ababababa", setting overlapping mode off will produce forward matches at offsets 0, 4. However when a backwards search is done, the results will be at offsets 6 and 2.

If matches searched for have boundary restrictions. BreakIterators can be used to define the valid boundaries of such a match. Once a BreakIterator is set, potential matches will be tested against the BreakIterator to determine if the boundaries are valid and that all characters in the potential match are equivalent to the pattern searched for. For example, looking for the pattern "fox" in the text "foxy fox" will produce match results at offset 0 and 5 with length 3 if no BreakIterators were set. However if a WordBreakIterator is set, the only match that would be found will be at the offset 5. Since, the SearchIterator guarantees that if a BreakIterator is set, all its matches will match the given pattern exactly, a potential match that passes the BreakIterator might still not produce a valid match. For instance the pattern "e" will not be found in the string "\u00e9" (latin small letter e with acute) if a CharacterBreakIterator is used. Even though "e" is a part of the character "\u00e9" and the potential match at offset 0 length 1 passes the CharacterBreakIterator test, "\u00e9" is not equivalent to "e", hence the SearchIterator rejects the potential match. By default, the SearchIterator does not impose any boundary restriction on the matches, it will return all results that match the pattern. Illustrating with the above example, "e" will be found in the string "\u00e9" if no BreakIterator is specified.

SearchIterator also provides a means to handle overlapping matches via the API setOverlapping(boolean). For example, if overlapping mode is set, searching for the pattern "abab" in the text "ababab" will match at positions 0 and 2, whereas if overlapping is not set, SearchIterator will only match at position 0. By default, overlapping mode is not set.

The APIs in SearchIterator are similar to that of other text iteration classes such as BreakIterator. Using this class, it is easy to scan through text looking for all occurances of a match.

Example of use:

 String target = "The quick brown fox jumped over the lazy fox";
 String pattern = "fox";
 SearchIterator iter = new StringSearch(pattern, target);
 for (int pos = iter.first(); pos != SearchIterator.DONE; 
                                                       pos = iter.next()) {
     // println matches at offset 16 and 41 with length 3
     System.out.println("Found match at " + pos + ", length is " 
                        + iter.getMatchLength());
 }
 target = "ababababa";
 pattern = "aba";
 iter.setTarget(new StringCharacterIterator(pattern));
 iter.setOverlapping(false);
 System.out.println("Overlapping mode set to false");
 System.out.println("Forward matches of pattern " + pattern + " in text "
                    + text + ": ");
 for (int pos = iter.first(); pos != SearchIterator.DONE; 
                                                       pos = iter.next()) {
     // println matches at offset 0 and 4 with length 3
     System.out.println("offset " + pos + ", length " 
                        + iter.getMatchLength());
 }
 System.out.println("Backward matches of pattern " + pattern + " in text "
                    + text + ": ");
 for (int pos = iter.last(); pos != SearchIterator.DONE; 
                                                    pos = iter.previous()) {
     // println matches at offset 6 and 2 with length 3
     System.out.println("offset " + pos + ", length " 
                        + iter.getMatchLength());
 }
 System.out.println("Overlapping mode set to true");
 System.out.println("Index set to 2");
 iter.setIndex(2);
 iter.setOverlapping(true);
 System.out.println("Forward matches of pattern " + pattern + " in text "
                    + text + ": ");
 for (int pos = iter.first(); pos != SearchIterator.DONE; 
                                                       pos = iter.next()) {
     // println matches at offset 2, 4 and 6 with length 3
     System.out.println("offset " + pos + ", length " 
                        + iter.getMatchLength());
 }
 System.out.println("Index set to 2");
 iter.setIndex(2);
 System.out.println("Backward matches of pattern " + pattern + " in text "
                    + text + ": ");
 for (int pos = iter.last(); pos != SearchIterator.DONE; 
                                                    pos = iter.previous()) {
     // println matches at offset 0 with length 3
     System.out.println("offset " + pos + ", length " 
                        + iter.getMatchLength());
 }
 
Author:
Laura Werner, synwee
See Also:
BreakIterator

Field Summary

static 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 BreakIterator
breakIterator
The BreakIterator to define the boundaries of a logical match.
protected int
matchLength
Length of the most current match in target text.
protected CharacterIterator
targetText
Target text for searching.

Constructor Summary

SearchIterator(CharacterIterator target, BreakIterator breaker)
Protected constructor for use by subclasses.

Method Summary

int
first()
Return the index of the first forward match in the target text.
int
following(int position)
Return the index of the first forward match in target text that is at or after argument position.
BreakIterator
getBreakIterator()
Returns the BreakIterator that is used to restrict the indexes at which matches are detected.
abstract int
getIndex()
Return the index in the target text at which the iterator is currently positioned.
int
getMatchLength()
Returns the length of the most recent match in the target text.
int
getMatchStart()
Returns the index of the most recent match in the target text.
String
getMatchedText()
Returns the text that was matched by the most recent call to first(), next(), previous(), or last().
CharacterIterator
getTarget()
Return the target text that is being searched.
protected abstract int
handleNext(int start)
Abstract method that subclasses override to provide the mechanism for finding the next forwards match in the target text.
protected abstract int
handlePrevious(int startAt)
Abstract method which subclasses override to provide the mechanism for finding the next backwards match in the target text.
boolean
isOverlapping()
Return true if the overlapping property has been set.
int
last()
Return the index of the first backward match in target text.
int
next()
Search forwards in the target text for the next valid match, starting the search from the current iterator position.
int
preceding(int position)
Return the index of the first backwards match in target text that ends at or before argument position.
int
previous()
Search backwards in the target text for the next valid match, starting the search from the current iterator position.
void
reset()
Resets the search iteration.
void
setBreakIterator(BreakIterator breakiter)
Set the BreakIterator that is used to restrict the points at which matches are detected.
void
setIndex(int position)
Sets the position in the target text at which the next search will start.
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.
void
setTarget(CharacterIterator text)
Set the target text to be searched.

Field Details

DONE

public 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.
Field Value:
-1

breakIterator

protected BreakIterator breakIterator
The BreakIterator to define the boundaries of a logical match. This value can be a null. See class documentation for more information.

matchLength

protected int matchLength
Length of the most current match in target text. Value 0 is the default value.

targetText

protected CharacterIterator targetText
Target text for searching.

Constructor Details

SearchIterator

protected SearchIterator(CharacterIterator target,
                         BreakIterator breaker)
Protected constructor for use by subclasses. Initializes the iterator with the argument target text for searching and sets the BreakIterator. See class documentation for more details on the use of the target text and BreakIterator.
Parameters:
target - The target text to be searched.
breaker - A BreakIterator that is used to determine the boundaries of a logical match. This argument can be null.
See Also:
BreakIterator

Method Details

first

public final int first()
Return the index of the first forward match in the target text. This method sets the iteration to begin at the start of the target text and searches forward from there.
Returns:
The index of the first forward match, or DONE if there are no matches.

following

public final int following(int position)
Return the index of the first forward match in target text that is at or after argument position. This method sets the iteration to begin at the specified position in the the target text and searches forward from there.
Returns:
The index of the first forward match, or DONE if there are no matches.

getBreakIterator

public BreakIterator getBreakIterator()
Returns the BreakIterator that is used to restrict the indexes at which matches are detected. This will be the same object that was passed to the constructor or to setBreakIterator. If the BreakIterator has not been set, null will be returned. See setBreakIterator for more information.
Returns:
the BreakIterator set to restrict logic matches

getIndex

public abstract int getIndex()
Returns:
index in the target text at which the iterator is currently positioned.

getMatchLength

public int getMatchLength()
Returns the length of the most recent match in the target text. This call returns a valid result only after a successful call to first(), next(), previous(), or last(). Just after construction, or after a searching method returns DONE, this method will return 0. See getMatchStart() for more details.
Returns:
The length of the most recent match in the target text, or 0 if there is no match.

getMatchStart

public int getMatchStart()
Returns the index of the most recent match in the target text. This call returns a valid result only after a successful call to first(), next(), previous(), or last(). Just after construction, or after a searching method returns DONE, this method will return DONE.

Use getMatchLength to get the length of the matched text. getMatchedText will return the subtext in the searched target text from index getMatchStart() with length getMatchLength().

Returns:
index to a substring within the text string that is being searched.

getMatchedText

public String getMatchedText()
Returns the text that was matched by the most recent call to first(), next(), previous(), or last(). If the iterator is not pointing at a valid match, for instance just after construction or after DONE has been returned, an empty String will be returned. See getMatchStart for more information
Returns:
the substring in the target text of the most recent match

getTarget

public CharacterIterator getTarget()
Return the target text that is being searched.
Returns:
target text being searched.

handleNext

protected abstract int handleNext(int start)
Parameters:
start - index in the target text at which the forwards search should begin.
Returns:
the starting index of the next forwards match if found, DONE otherwise

handlePrevious

protected abstract int handlePrevious(int startAt)
Parameters:
startAt - index in the target text at which the backwards search should begin.
Returns:
the starting index of the next backwards match if found, DONE otherwise

isOverlapping

public boolean isOverlapping()
Return true if the overlapping property has been set. See setOverlapping(boolean) for more information.
Returns:
true if the overlapping property has been set, false otherwise

last

public final int last()
Return the index of the first backward match in target text. This method sets the iteration to begin at the end of the target text and searches backwards from there.
Returns:
The starting index of the first backward match, or DONE if there are no matches.

next

public int next()
Search forwards in the target text for the next valid match, starting the search from the current iterator position. The iterator is adjusted so that its current index, as returned by getIndex(), is the starting position of the match if one was found. If a match is found, the index of the match is returned, otherwise DONE is returned. If overlapping mode is set, the beginning of the found match can be before the end of the current match, if any.
Returns:
The starting index of the next forward match after the current iterator position, or DONE if there are no more matches.

preceding

public final int preceding(int position)
Return the index of the first backwards match in target text that ends at or before argument position. This method sets the iteration to begin at the argument position index of the target text and searches backwards from there.
Returns:
The starting index of the first backwards match, or DONE if there are no matches.

previous

public int previous()
Search backwards in the target text for the next valid match, starting the search from the current iterator position. The iterator is adjusted so that its current index, as returned by getIndex(), is the starting position of the match if one was found. If a match is found, the index is returned, otherwise DONE is returned. If overlapping mode is set, the end of the found match can be after the beginning of the previous match, if any.
Returns:
The starting index of the next backwards match after the current iterator position, or DONE if there are no more matches.

reset

public void reset()
Resets the search iteration. All properties will be reset to their default values.

If a forward iteration is initiated, the next search will begin at the start of the target text. Otherwise, if a backwards iteration is initiated, the next search will begin at the end of the target text.


setBreakIterator

public void setBreakIterator(BreakIterator breakiter)
Set the BreakIterator that is used to restrict the points at which matches are detected. Using null as the parameter is legal; it means that break detection should not be attempted. See class documentation for more information.
Parameters:
breakiter - A BreakIterator that will be used to restrict the points at which matches are detected.

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.
Parameters:
position - position from which to start the next search

setMatchLength

protected void setMatchLength(int length)
Sets the length of the most recent match in the target text. Subclasses' handleNext() and handlePrevious() methods should call this after they find a match in the target text.
Parameters:
length - new length to set

setOverlapping

public void setOverlapping(boolean allowOverlap)
Determines whether overlapping matches are returned. See the class documentation for more information about overlapping matches.

The default setting of this property is false

Parameters:
allowOverlap - flag indicator if overlapping matches are allowed

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.
Parameters:
text - new text iterator to look for match,

Copyright (c) 2006 IBM Corporation and others.