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());
}
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.
- 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.
- 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.
- the BreakIterator set to restrict logic matches
getIndex
public abstract int getIndex()
Return the index in the target text at which the iterator is currently
positioned.
If the iteration has gone past the end of the target text, or past
the beginning for a backwards search,
DONE
is returned.
- 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.
- 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().
- 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
- the substring in the target text of the most recent match
getTarget
public CharacterIterator getTarget()
Return the target text that is being searched.
- target text being searched.
handleNext
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. This
allows different subclasses to provide different search algorithms.
If a match is found, this function must call setMatchLength(int) to
set the length of the result match.
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 not found,
DONE will be returned.
start
- index in the target text at which the forwards search
should begin.
- the starting index of the next forwards match if found, DONE
otherwise
handlePrevious
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.
This allows different
subclasses to provide different search algorithms.
If a match is found, this function must call setMatchLength(int) to
set the length of the result match.
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 not found,
DONE will be returned.
startAt
- index in the target text at which the backwards search
should begin.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
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.
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.
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
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.
text
- new text iterator to look for match,