Cloneable
public abstract class BreakIterator extends Object implements Cloneable
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 getWordInstance
, getLineInstance
, getSentenceInstance
, and getCharacterInstance
to create BreakIterator
s 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. Actual line breaking needs to also consider the available line width and is handled by higher-level software.
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 through character strings, regardless of how the character is stored. The boundaries returned may be those of supplementary characters, combining character sequences, or ligature clusters. 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.
The BreakIterator
instances returned by the factory methods of this class are intended for use with natural languages only, not for programming language text. It is however possible to define subclasses that tokenize a programming language.
Examples:
Creating and using text boundaries:
Print each element in order: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 reverse 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 first element: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 last 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 the element at a specified position:public static void printLast(BreakIterator boundary, String source) { int end = boundary.last(); int start = boundary.previous(); System.out.println(source.substring(start,end)); }
Find the next word: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)); }
(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.)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.codePointAt(p))) return last; } last = current; current = wb.next(); } return BreakIterator.DONE; }
Modifier and Type | Field | Description |
---|---|---|
static final int |
DONE |
DONE is returned by previous(), next(), next(int), preceding(int) and following(int) when either the first or last text boundary has been reached. |
Modifier | Constructor | Description |
---|---|---|
protected |
Constructor. |
Modifier and Type | Method | Description |
---|---|---|
Object |
clone() |
Create a copy of this iterator |
abstract int |
current() |
Returns character index of the text boundary that was most recently returned by next(), next(int), previous(), first(), last(), following(int) or preceding(int). |
abstract int |
first() |
Returns the first boundary. |
abstract int |
following |
Returns the first boundary following the specified character offset. |
static Locale[] |
getAvailableLocales() |
Returns an array of all locales for which the get*Instance methods of this class can return localized instances. |
static BreakIterator |
getCharacterInstance() |
|
static BreakIterator |
getCharacterInstance |
Returns a new BreakIterator instance for character breaks for the given locale. |
static BreakIterator |
getLineInstance() |
|
static BreakIterator |
getLineInstance |
Returns a new BreakIterator instance for line breaks for the given locale. |
static BreakIterator |
getSentenceInstance() |
|
static BreakIterator |
getSentenceInstance |
Returns a new BreakIterator instance for sentence breaks for the given locale. |
abstract CharacterIterator |
getText() |
Get the text being scanned |
static BreakIterator |
getWordInstance() |
|
static BreakIterator |
getWordInstance |
Returns a new BreakIterator instance for word breaks for the given locale. |
boolean |
isBoundary |
Returns true if the specified character offset is a text boundary. |
abstract int |
last() |
Returns the last boundary. |
abstract int |
next() |
Returns the boundary following the current boundary. |
abstract int |
next |
Returns the nth boundary from the current boundary. |
int |
preceding |
Returns the last boundary preceding the specified character offset. |
abstract int |
previous() |
Returns the boundary preceding the current boundary. |
void |
setText |
Set a new text string to be scanned. |
abstract void |
setText |
Set a new text for scanning. |
public static final int DONE
protected BreakIterator()
public Object clone()
public abstract int first()
public abstract int last()
public abstract int next(int n)
BreakIterator.DONE
and the current position is set to either the first or last text boundary depending on which one is reached. Otherwise, the iterator's current position is set to the new boundary. For example, if the iterator's current position is the mth text boundary and three more boundaries exist from the current boundary to the last text boundary, the next(2) call will return m + 2. The new text position is set to the (m + 2)th text boundary. A next(4) call would return BreakIterator.DONE
and the last text boundary would become the new text position.n
- which boundary to return. A value of 0 does nothing. Negative values move to previous boundaries and positive values move to later boundaries.BreakIterator.DONE
if either first or last text boundary has been reached.public abstract int next()
BreakIterator.DONE
and the iterator's current position is unchanged. Otherwise, the iterator's current position is set to the boundary following the current boundary.BreakIterator.DONE
if the current boundary is the last text boundary. Equivalent to next(1).public abstract int previous()
BreakIterator.DONE
and the iterator's current position is unchanged. Otherwise, the iterator's current position is set to the boundary preceding the current boundary.BreakIterator.DONE
if the current boundary is the first text boundary.public abstract int following(int offset)
BreakIterator.DONE
and the iterator's current position is unchanged. Otherwise, the iterator's current position is set to the returned boundary. The value returned is always greater than the offset or the value BreakIterator.DONE
.offset
- the character offset to begin scanning.BreakIterator.DONE
if the last text boundary is passed in as the offset.IllegalArgumentException
- if the specified offset is less than the first text boundary or greater than the last text boundary.public int preceding(int offset)
BreakIterator.DONE
and the iterator's current position is unchanged. Otherwise, the iterator's current position is set to the returned boundary. The value returned is always less than the offset or the value BreakIterator.DONE
.offset
- the character offset to begin scanning.BreakIterator.DONE
if the first text boundary is passed in as the offset.IllegalArgumentException
- if the specified offset is less than the first text boundary or greater than the last text boundary.public boolean isBoundary(int offset)
offset
- the character offset to check.true
if "offset" is a boundary position, false
otherwise.IllegalArgumentException
- if the specified offset is less than the first text boundary or greater than the last text boundary.public abstract int current()
BreakIterator.DONE
because either first or last text boundary has been reached, it returns the first or last text boundary depending on which one is reached.public abstract CharacterIterator getText()
public void setText(String newText)
newText
- new text to scan.public abstract void setText(CharacterIterator newText)
newText
- new text to scan.public static BreakIterator getWordInstance()
public static BreakIterator getWordInstance(Locale locale)
BreakIterator
instance for word breaks for the given locale.locale
- the desired localeNullPointerException
- if locale
is nullpublic static BreakIterator getLineInstance()
public static BreakIterator getLineInstance(Locale locale)
BreakIterator
instance for line breaks for the given locale.locale
- the desired localeNullPointerException
- if locale
is nullpublic static BreakIterator getCharacterInstance()
public static BreakIterator getCharacterInstance(Locale locale)
BreakIterator
instance for character breaks for the given locale.locale
- the desired localeNullPointerException
- if locale
is nullpublic static BreakIterator getSentenceInstance()
public static BreakIterator getSentenceInstance(Locale locale)
BreakIterator
instance for sentence breaks for the given locale.locale
- the desired localeNullPointerException
- if locale
is nullpublic static Locale[] getAvailableLocales()
get*Instance
methods of this class can return localized instances. The returned array represents the union of locales supported by the Java runtime and by installed BreakIteratorProvider
implementations. At a minimum, the returned array must contain a Locale
instance equal to Locale.ROOT
and a Locale
instance equal to Locale.US
.BreakIterator
instances are available.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/text/BreakIterator.html