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java.text

public abstract Class BreakIterator

extends Object
implements Cloneable
Class Inheritance
All Implemented Interfaces
java.lang.Cloneable
Known Direct Subclasses
sun.util.locale.provider.BreakIteratorProviderImpl.GraphemeBreakIterator, sun.text.RuleBasedBreakIterator
Imports
java.lang.ref.SoftReference, java.text.spi.BreakIteratorProvider, java.util.Locale, sun.util.locale.provider.LocaleProviderAdapter, .LocaleServiceProviderPool

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 getWordInstance, getLineInstance, getSentenceInstance, and getCharacterInstance 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. 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.

Implementation Specification

The default implementation of the character boundary analysis conforms to the Unicode Consortium's Extended Grapheme Cluster breaks. For more detail, refer to Grapheme Cluster Boundaries section in the Unicode Standard Annex #29.

Implementation Note

The default implementations of BreakIterator will perform the equivalent of calling setText("") if the text hasn't been set by either setText(String) or setText(CharacterIterator) and a boundary searching operation is called by the BreakIterator instance. 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:

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); } }
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)); } }
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)); } }
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)); }
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)); }
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)); }
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.codePointAt(p))) return last; } last = current; current = wb.next(); } return BreakIterator.DONE; }
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;
}
(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.)
Since
1.1
See Also
CharacterIterator

Nested and Inner Type Summary

Modifier and TypeClass and Description
private static class

Field Summary

Modifier and TypeField and Description
private static final int
public 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.

private static final SoftReference<BreakIterator.BreakIteratorCache>[]
private static final int
private static final int
private static final int

Constructor Summary

AccessConstructor and Description
protected
BreakIterator()

Constructor.

Method Summary

Modifier and TypeMethod and Description
public Object

Returns:

A copy of this
clone
()

Overrides java.lang.Object.clone.

Create a copy of this iterator

private static BreakIterator
createBreakInstance(Locale locale, int type)

private static BreakIterator
public abstract int

Returns:

The text boundary returned from the above methods, first or last text boundary.
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).

public abstract int

Returns:

The character index of the first text boundary.
first
()

Returns the first boundary.

public abstract int

Returns:

The first boundary after the specified offset or BreakIterator.DONE if the last text boundary is passed in as the offset.
following
(int
the character offset to begin scanning.
offset
)

Returns the first boundary following the specified character offset.

public static synchronized Locale[]

Returns:

An array of locales for which localized BreakIterator instances are available.
getAvailableLocales
()

Returns an array of all locales for which the get*Instance methods of this class can return localized instances.

private static BreakIterator
getBreakInstance(Locale locale, int type)

public static BreakIterator

Returns:

A break iterator for character breaks
getCharacterInstance
()

Returns a new BreakIterator instance for character breaks for the default locale.

public static BreakIterator

Returns:

A break iterator for character breaks
getCharacterInstance
(Locale
the desired locale
locale
)

Returns a new BreakIterator instance for character breaks for the given locale.

public static BreakIterator

Returns:

A break iterator for line breaks
getLineInstance
()

Returns a new BreakIterator instance for line breaks for the default locale.

public static BreakIterator

Returns:

A break iterator for line breaks
getLineInstance
(Locale
the desired locale
locale
)

Returns a new BreakIterator instance for line breaks for the given locale.

public static BreakIterator

Returns:

A break iterator for sentence breaks
getSentenceInstance
()

Returns a new BreakIterator instance for sentence breaks for the default locale.

public static BreakIterator

Returns:

A break iterator for sentence breaks
getSentenceInstance
(Locale
the desired locale
locale
)

Returns a new BreakIterator instance for sentence breaks for the given locale.

public abstract CharacterIterator

Returns:

the text being scanned
getText
()

Get the text being scanned

public static BreakIterator

Returns:

A break iterator for word breaks
getWordInstance
()

Returns a new BreakIterator instance for word breaks for the default locale.

public static BreakIterator

Returns:

A break iterator for word breaks
getWordInstance
(Locale
the desired locale
locale
)

Returns a new BreakIterator instance for word breaks for the given locale.

public boolean

Returns:

true if "offset" is a boundary position, false otherwise.
isBoundary
(int
the character offset to check.
offset
)

Returns true if the specified character offset is a text boundary.

public abstract int

Returns:

The character index of the last text boundary.
last
()

Returns the last boundary.

public abstract int

Returns:

The character index of the nth boundary from the current position or BreakIterator.DONE if either first or last text boundary has been reached.
next
(int
which boundary to return. A value of 0 does nothing. Negative values move to previous boundaries and positive values move to later boundaries.
n
)

Returns the nth boundary from the current boundary.

public abstract int

Returns:

The character index of the next text boundary or BreakIterator.DONE if the current boundary is the last text boundary. Equivalent to next(1).
next
()

Returns the boundary following the current boundary.

public int

Returns:

The last boundary before the specified offset or BreakIterator.DONE if the first text boundary is passed in as the offset.
preceding
(int
the character offset to begin scanning.
offset
)

Returns the last boundary preceding the specified character offset.

public abstract int

Returns:

The character index of the previous text boundary or BreakIterator.DONE if the current boundary is the first text boundary.
previous
()

Returns the boundary preceding the current boundary.

public void
setText(String
new text to scan.
newText
)

Set a new text string to be scanned.

public abstract void
setText(CharacterIterator
new text to scan.
newText
)

Set a new text for scanning.

Inherited from java.lang.Object:
equalsfinalizegetClasshashCodenotifynotifyAlltoStringwaitwaitwait

Field Detail

CHARACTER_INDEXback to summary
private static final int CHARACTER_INDEX
DONEback to summary
public 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.

iterCacheback to summary
private static final SoftReference<BreakIterator.BreakIteratorCache>[] iterCache
Annotations
@SuppressWarnings:unchecked
LINE_INDEXback to summary
private static final int LINE_INDEX
SENTENCE_INDEXback to summary
private static final int SENTENCE_INDEX
WORD_INDEXback to summary
private static final int WORD_INDEX

Constructor Detail

BreakIteratorback to summary
protected BreakIterator()

Constructor. BreakIterator is stateless and has no default behavior.

Method Detail

cloneback to summary
public Object clone()

Overrides java.lang.Object.clone.

Create a copy of this iterator

Returns:Object

A copy of this

Annotations
@Override
createBreakInstanceback to summary
private static BreakIterator createBreakInstance(Locale locale, int type)
createBreakInstanceback to summary
private static BreakIterator createBreakInstance(LocaleProviderAdapter adapter, Locale locale, int type)
currentback to summary
public 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). If any of these methods returns 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.

Returns:int

The text boundary returned from the above methods, first or last text boundary.

See Also
next(), next(int), previous(), first(), last(), following(int), preceding(int)
firstback to summary
public abstract int first()

Returns the first boundary. The iterator's current position is set to the first text boundary.

Returns:int

The character index of the first text boundary.

followingback to summary
public abstract int following(int offset)

Returns the first boundary following the specified character offset. If the specified offset is equal to the last text boundary, it returns 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.

Parameters
offset:int

the character offset to begin scanning.

Returns:int

The first boundary after the specified offset or BreakIterator.DONE if the last text boundary is passed in as the offset.

Exceptions
IllegalArgumentException:
if the specified offset is less than the first text boundary or greater than the last text boundary.
getAvailableLocalesback to summary
public static synchronized Locale[] getAvailableLocales()

Returns an array of all locales for which the 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.

Returns:Locale[]

An array of locales for which localized BreakIterator instances are available.

getBreakInstanceback to summary
private static BreakIterator getBreakInstance(Locale locale, int type)
getCharacterInstanceback to summary
public static BreakIterator getCharacterInstance()

Returns a new BreakIterator instance for character breaks for the default locale.

Returns:BreakIterator

A break iterator for character breaks

getCharacterInstanceback to summary
public static BreakIterator getCharacterInstance(Locale locale)

Returns a new BreakIterator instance for character breaks for the given locale.

Parameters
locale:Locale

the desired locale

Returns:BreakIterator

A break iterator for character breaks

Exceptions
NullPointerException:
if locale is null
getLineInstanceback to summary
public static BreakIterator getLineInstance()

Returns a new BreakIterator instance for line breaks for the default locale.

Returns:BreakIterator

A break iterator for line breaks

getLineInstanceback to summary
public static BreakIterator getLineInstance(Locale locale)

Returns a new BreakIterator instance for line breaks for the given locale.

Parameters
locale:Locale

the desired locale

Returns:BreakIterator

A break iterator for line breaks

Exceptions
NullPointerException:
if locale is null
getSentenceInstanceback to summary
public static BreakIterator getSentenceInstance()

Returns a new BreakIterator instance for sentence breaks for the default locale.

Returns:BreakIterator

A break iterator for sentence breaks

getSentenceInstanceback to summary
public static BreakIterator getSentenceInstance(Locale locale)

Returns a new BreakIterator instance for sentence breaks for the given locale.

Parameters
locale:Locale

the desired locale

Returns:BreakIterator

A break iterator for sentence breaks

Exceptions
NullPointerException:
if locale is null
getTextback to summary
public abstract CharacterIterator getText()

Get the text being scanned

Returns:CharacterIterator

the text being scanned

getWordInstanceback to summary
public static BreakIterator getWordInstance()

Returns a new BreakIterator instance for word breaks for the default locale.

Returns:BreakIterator

A break iterator for word breaks

getWordInstanceback to summary
public static BreakIterator getWordInstance(Locale locale)

Returns a new BreakIterator instance for word breaks for the given locale.

Parameters
locale:Locale

the desired locale

Returns:BreakIterator

A break iterator for word breaks

Exceptions
NullPointerException:
if locale is null
isBoundaryback to summary
public boolean isBoundary(int offset)

Returns true if the specified character offset is a text boundary.

Parameters
offset:int

the character offset to check.

Returns:boolean

true if "offset" is a boundary position, false otherwise.

Exceptions
IllegalArgumentException:
if the specified offset is less than the first text boundary or greater than the last text boundary.
Since
1.2
lastback to summary
public abstract int last()

Returns the last boundary. The iterator's current position is set to the last text boundary.

Returns:int

The character index of the last text boundary.

nextback to summary
public abstract int next(int n)

Returns the nth boundary from the current boundary. If either the first or last text boundary has been reached, it returns 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.

Parameters
n:int

which boundary to return. A value of 0 does nothing. Negative values move to previous boundaries and positive values move to later boundaries.

Returns:int

The character index of the nth boundary from the current position or BreakIterator.DONE if either first or last text boundary has been reached.

nextback to summary
public abstract int next()

Returns the boundary following the current boundary. If the current boundary is the last text boundary, it returns 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.

Returns:int

The character index of the next text boundary or BreakIterator.DONE if the current boundary is the last text boundary. Equivalent to next(1).

See Also
next(int)
precedingback to summary
public int preceding(int offset)

Returns the last boundary preceding the specified character offset. If the specified offset is equal to the first text boundary, it returns 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.

Parameters
offset:int

the character offset to begin scanning.

Returns:int

The last boundary before the specified offset or BreakIterator.DONE if the first text boundary is passed in as the offset.

Exceptions
IllegalArgumentException:
if the specified offset is less than the first text boundary or greater than the last text boundary.
Since
1.2
previousback to summary
public abstract int previous()

Returns the boundary preceding the current boundary. If the current boundary is the first text boundary, it returns 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.

Returns:int

The character index of the previous text boundary or BreakIterator.DONE if the current boundary is the first text boundary.

setTextback to summary
public void setText(String newText)

Set a new text string to be scanned. The current scan position is reset to first().

Parameters
newText:String

new text to scan.

setTextback to summary
public abstract void setText(CharacterIterator newText)

Set a new text for scanning. The current scan position is reset to first().

Parameters
newText:CharacterIterator

new text to scan.

java.text back to summary

private final Class BreakIterator.BreakIteratorCache

extends Object
Class Inheritance

Field Summary

Modifier and TypeField and Description
private BreakIterator
private Locale

Constructor Summary

AccessConstructor and Description
pack-priv

Method Summary

Modifier and TypeMethod and Description
pack-priv BreakIterator
pack-priv Locale
Inherited from java.lang.Object:
cloneequalsfinalizegetClasshashCodenotifynotifyAlltoStringwaitwaitwait

Field Detail

iterback to summary
private BreakIterator iter
localeback to summary
private Locale locale

Constructor Detail

BreakIteratorCacheback to summary
pack-priv BreakIteratorCache(Locale locale, BreakIterator iter)

Method Detail

createBreakInstanceback to summary
pack-priv BreakIterator createBreakInstance()
getLocaleback to summary
pack-priv Locale getLocale()