public
abstract
class
BreakIterator
extends Object
implements
Cloneable
java.lang.Object | |
↳ | java.text.BreakIterator |
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 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)); }
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.)
See also:
Constants | |
---|---|
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. |
Protected constructors | |
---|---|
BreakIterator()
Constructor. |
Public methods | |
---|---|
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(int offset)
Returns the first boundary following the specified character offset. |
static
Locale[]
|
getAvailableLocales()
Returns an array of all locales for which the
|
static
BreakIterator
|
getCharacterInstance(Locale locale)
Returns a new |
static
BreakIterator
|
getCharacterInstance()
Returns a new |
static
BreakIterator
|
getLineInstance(Locale locale)
Returns a new |
static
BreakIterator
|
getLineInstance()
Returns a new |
static
BreakIterator
|
getSentenceInstance(Locale locale)
Returns a new |
static
BreakIterator
|
getSentenceInstance()
Returns a new |
abstract
CharacterIterator
|
getText()
Get the text being scanned |
static
BreakIterator
|
getWordInstance()
Returns a new |
static
BreakIterator
|
getWordInstance(Locale locale)
Returns a new |
boolean
|
isBoundary(int offset)
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(int n)
Returns the nth boundary from the current boundary. |
int
|
preceding(int offset)
Returns the last boundary preceding the specified character offset. |
abstract
int
|
previous()
Returns the boundary preceding the current boundary. |
void
|
setText(String newText)
Set a new text string to be scanned. |
abstract
void
|
setText(CharacterIterator newText)
Set a new text for scanning. |
Inherited methods | |
---|---|
From
class
java.lang.Object
|
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.
Constant Value: -1 (0xffffffff)
BreakIterator ()
Constructor. BreakIterator is stateless and has no default behavior.
Object clone ()
Create a copy of this iterator
Returns | |
---|---|
Object |
A copy of this |
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. |
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. |
int following (int offset)
Returns the first boundary following the specified character offset. If the
specified offset equals 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. |
Throws | |
---|---|
IllegalArgumentException |
if the specified offset is less than the first text boundary or greater than the last text boundary. |
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.
It must contain at least a Locale
instance equal to Locale.US
.
Returns | |
---|---|
Locale[] |
An array of locales for which localized
BreakIterator instances are available.
|
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 |
Throws | |
---|---|
NullPointerException |
if locale is null
|
BreakIterator getCharacterInstance ()
Returns a new BreakIterator
instance
for character breaks
for the default locale.
Returns | |
---|---|
BreakIterator |
A break iterator for character breaks |
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 |
Throws | |
---|---|
NullPointerException |
if locale is null
|
BreakIterator getLineInstance ()
Returns a new BreakIterator
instance
for line breaks
for the default locale.
Returns | |
---|---|
BreakIterator |
A break iterator for line breaks |
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 |
Throws | |
---|---|
NullPointerException |
if locale is null
|
BreakIterator getSentenceInstance ()
Returns a new BreakIterator
instance
for sentence breaks
for the default locale.
Returns | |
---|---|
BreakIterator |
A break iterator for sentence breaks |
CharacterIterator getText ()
Get the text being scanned
Returns | |
---|---|
CharacterIterator |
the text being scanned |
BreakIterator getWordInstance ()
Returns a new BreakIterator
instance
for word breaks
for the default locale.
Returns | |
---|---|
BreakIterator |
A break iterator for word breaks |
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 |
Throws | |
---|---|
NullPointerException |
if locale is null
|
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. |
Throws | |
---|---|
IllegalArgumentException |
if the specified offset is less than the first text boundary or greater than the last text boundary. |
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. |
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:
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.
|
int preceding (int offset)
Returns the last boundary preceding the specified character offset. If the
specified offset equals 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 characater 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. |
Throws | |
---|---|
IllegalArgumentException |
if the specified offset is less than the first text boundary or greater than the last text boundary. |
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.
|
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.
|
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.
|