The BreakIterator class implements methods for finding
the location of boundaries in text. Instances of BreakIterator
maintain a current position and scan over text
returning the index of characters where boundaries occur.
Internally, BreakIterator scans text using a
CharacterIterator, and is thus able to scan text held
by any object implementing that protocol. A StringCharacterIterator
is used to scan String objects passed to setText.
You use the factory methods provided by this class to create
instances of various types of break iterators. In particular,
use getWordIterator, getLineIterator,
getSentenceIterator, and getCharacterIterator
to create BreakIterators that perform
word, line, sentence, and character boundary analysis respectively.
A single BreakIterator can work only on one unit
(word, line, sentence, and so on). You must use a different iterator
for each unit boundary analysis you wish to perform.
Line boundary analysis determines where a text string can be
broken when line-wrapping. The mechanism correctly handles
punctuation and hyphenated words.
Sentence boundary analysis allows selection with correct interpretation
of periods within numbers and abbreviations, and trailing punctuation
marks such as quotation marks and parentheses.
Word boundary analysis is used by search and replace functions, as
well as within text editing applications that allow the user to
select words with a double click. Word selection provides correct
interpretation of punctuation marks within and following
words. Characters that are not part of a word, such as symbols
or punctuation marks, have word-breaks on both sides.
Character boundary analysis allows users to interact with characters
as they expect to, for example, when moving the cursor through a text
string. Character boundary analysis provides correct navigation of
through character strings, regardless of how the character is stored.
For example, an accented character might be stored as a base character
and a diacritical mark. What users consider to be a character can
differ between languages.
BreakIterator is intended for use with natural
languages only. Do not use this class to tokenize a programming language.
Examples:
Creating and using text boundaries
public static void main(String args[]) {
if (args.length == 1) {
String stringToExamine = args[0];
//print each word in order
BreakIterator boundary = BreakIterator.getWordInstance();
boundary.setText(stringToExamine);
printEachForward(boundary, stringToExamine);
//print each sentence in reverse order
boundary = BreakIterator.getSentenceInstance(Locale.US);
boundary.setText(stringToExamine);
printEachBackward(boundary, stringToExamine);
printFirst(boundary, stringToExamine);
printLast(boundary, stringToExamine);
}
}
Print each element in order
public static void printEachForward(BreakIterator boundary, String source) {
int start = boundary.first();
for (int end = boundary.next();
end != BreakIterator.DONE;
start = end, end = boundary.next()) {
System.out.println(source.substring(start,end));
}
}
Print each element in reverse order
public static void printEachBackward(BreakIterator boundary, String source) {
int end = boundary.last();
for (int start = boundary.previous();
start != BreakIterator.DONE;
end = start, start = boundary.previous()) {
System.out.println(source.substring(start,end));
}
}
Print first element
public static void printFirst(BreakIterator boundary, String source) {
int start = boundary.first();
int end = boundary.next();
System.out.println(source.substring(start,end));
}
Print last element
public static void printLast(BreakIterator boundary, String source) {
int end = boundary.last();
int start = boundary.previous();
System.out.println(source.substring(start,end));
}
Print the element at a specified position
public static void printAt(BreakIterator boundary, int pos, String source) {
int end = boundary.following(pos);
int start = boundary.previous();
System.out.println(source.substring(start,end));
}
Find the next word
public static int nextWordStartAfter(int pos, String text) {
BreakIterator wb = BreakIterator.getWordInstance();
wb.setText(text);
int last = wb.following(pos);
int current = wb.next();
while (current != BreakIterator.DONE) {
for (int p = last; p < current; p++) {
if (Character.isLetter(text.charAt(p))
return last;
}
last = current;
current = wb.next();
}
return BreakIterator.DONE;
}
(The iterator returned by BreakIterator.getWordInstance() is unique in that
the break positions it returns don't represent both the start and end of the
thing being iterated over. That is, a sentence-break iterator returns breaks
that each represent the end of one sentence and the beginning of the next.
With the word-break iterator, the characters between two boundaries might be a
word, or they might be the punctuation or whitespace between two words. The
above code uses a simple heuristic to determine which boundary is the beginning
of a word: If the characters between this boundary and the next boundary
include at least one letter (this can be an alphabetical letter, a CJK ideograph,
a Hangul syllable, a Kana character, etc.), then the text between this boundary
and the next is a word; otherwise, it's the material between words.)
getCharacterInstance()
Create BreakIterator for character-breaks using default locale
Returns an instance of a BreakIterator implementing character breaks.
getCharacterInstance(Locale where)
Create BreakIterator for character-breaks using specified locale
Returns an instance of a BreakIterator implementing character breaks.
getSentenceInstance()
Create BreakIterator for sentence-breaks using default locale
Returns an instance of a BreakIterator implementing sentence breaks.
getSentenceInstance(Locale where)
Create BreakIterator for sentence-breaks using specified locale
Returns an instance of a BreakIterator implementing sentence breaks.
Return the first boundary. The iterator's current position is set
to the first boundary.
Returns:
The character index of the first text boundary.
last
public abstract int last()
Return the last boundary. The iterator's current position is set
to the last boundary.
Returns:
The character index of the last text boundary.
next
public abstract int next(int n)
Return the nth boundary from the current boundary
Parameters:
n - which boundary to return. A value of 0
does nothing. Negative values move to previous boundaries
and positive values move to later boundaries.
Returns:
The index of the nth boundary from the current position.
next
public abstract int next()
Return the boundary following the current boundary.
Returns:
The character index of the next text boundary or DONE if all
boundaries have been returned. Equivalent to next(1).
previous
public abstract int previous()
Return the boundary preceding the current boundary.
Returns:
The character index of the previous text boundary or DONE if all
boundaries have been returned.
following
public abstract int following(int offset)
Return the first boundary following the specified offset.
The value returned is always greater than the offset or
the value BreakIterator.DONE
Parameters:
offset - the offset to begin scanning. Valid values
are determined by the CharacterIterator passed to
setText(). Invalid values cause
an IllegalArgumentException to be thrown.
Returns:
The first boundary after the specified offset.
preceding
public int preceding(int offset)
Return the last boundary preceding the specfied offset.
The value returned is always less than the offset or the value
BreakIterator.DONE.
Parameters:
offset - the offset to begin scanning. Valid values are
determined by the CharacterIterator passed to setText().
Invalid values cause an IllegalArgumentException to be thrown.
Returns:
The last boundary before the specified offset.
isBoundary
public boolean isBoundary(int offset)
Return true if the specified position is a boundary position.
Parameters:
offset - the offset to check.
Returns:
True if "offset" is a boundary position.
current
public abstract int current()
Return character index of the text boundary that was most recently
returned by next(), previous(), first(), or last()
Create BreakIterator for word-breaks using default locale.
Returns an instance of a BreakIterator implementing word breaks.
WordBreak is usefull for word selection (ex. double click)
Create BreakIterator for word-breaks using specified locale.
Returns an instance of a BreakIterator implementing word breaks.
WordBreak is usefull for word selection (ex. double click)
Parameters:
where - the local. If a specific WordBreak is not
avaliable for the specified locale, a default WordBreak is returned.
Create BreakIterator for line-breaks using default locale.
Returns an instance of a BreakIterator implementing line breaks. Line
breaks are logically possible line breaks, actual line breaks are
usually determined based on display width.
LineBreak is useful for word wrapping text.
Create BreakIterator for line-breaks using specified locale.
Returns an instance of a BreakIterator implementing line breaks. Line
breaks are logically possible line breaks, actual line breaks are
usually determined based on display width.
LineBreak is useful for word wrapping text.
Parameters:
where - the local. If a specific LineBreak is not
avaliable for the specified locale, a default LineBreak is returned.
Create BreakIterator for character-breaks using default locale
Returns an instance of a BreakIterator implementing character breaks.
Character breaks are boundaries of combining character sequences.
Create BreakIterator for character-breaks using specified locale
Returns an instance of a BreakIterator implementing character breaks.
Character breaks are boundaries of combining character sequences.
Parameters:
where - the local. If a specific character break is not
avaliable for the specified local, a default character break is returned.
Submit a bug or feature For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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