JavaTM 2 Platform Std. Ed. v1.5.0
java.text
Class BreakIterator
java.lang.Object
java.text.BreakIterator
- All Implemented Interfaces:
- Cloneable
public abstract class BreakIterator - extends Object
- implements Cloneable
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 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.
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.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:
CharacterIterator
Field Summary |
static int |
DONE
DONE is returned by previous() and next() after all valid
boundaries have been returned. |
Method Summary |
Object |
clone()
Create a copy of this iterator |
abstract int |
current()
Return character index of the text boundary that was most recently
returned by next(), previous(), first(), or last() |
abstract int |
first()
Return the first boundary. |
abstract int |
following(int offset)
Return the first boundary following the specified 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()
Create BreakIterator for character-breaks using default locale
Returns an instance of a BreakIterator implementing character breaks. |
static BreakIterator |
getCharacterInstance(Locale where)
Create BreakIterator for character-breaks using specified locale
Returns an instance of a BreakIterator implementing character breaks. |
protected static int |
getInt(byte[] buf,
int offset)
|
static BreakIterator |
getLineInstance()
Create BreakIterator for line-breaks using default locale. |
static BreakIterator |
getLineInstance(Locale where)
Create BreakIterator for line-breaks using specified locale. |
protected static long |
getLong(byte[] buf,
int offset)
|
static BreakIterator |
getSentenceInstance()
Create BreakIterator for sentence-breaks using default locale
Returns an instance of a BreakIterator implementing sentence breaks. |
static BreakIterator |
getSentenceInstance(Locale where)
Create BreakIterator for sentence-breaks using specified locale
Returns an instance of a BreakIterator implementing sentence breaks. |
protected static short |
getShort(byte[] buf,
int offset)
|
abstract CharacterIterator |
getText()
Get the text being scanned |
static BreakIterator |
getWordInstance()
Create BreakIterator for word-breaks using default locale. |
static BreakIterator |
getWordInstance(Locale where)
Create BreakIterator for word-breaks using specified locale. |
boolean |
isBoundary(int offset)
Return true if the specified position is a boundary position. |
abstract int |
last()
Return the last boundary. |
abstract int |
next()
Return the boundary following the current boundary. |
abstract int |
next(int n)
Return the nth boundary from the current boundary |
int |
preceding(int offset)
Return the last boundary preceding the specfied offset. |
abstract int |
previous()
Return the boundary preceding the current boundary. |
abstract void |
setText(CharacterIterator newText)
Set a new text for scanning. |
void |
setText(String newText)
Set a new text string to be scanned. |
DONE
public static final int DONE
- DONE is returned by previous() and next() after all valid
boundaries have been returned.
- See Also:
- Constant Field Values
BreakIterator
protected BreakIterator()
- Constructor. BreakIterator is stateless and has no default behavior.
clone
public Object clone()
- Create a copy of this iterator
- Overrides:
clone in class Object
- Returns:
- A copy of this
- See Also:
Cloneable
first
public abstract int first()
- 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.
- Since:
- 1.2
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.
- Since:
- 1.2
current
public abstract int current()
- Return character index of the text boundary that was most recently
returned by next(), previous(), first(), or last()
- Returns:
- The boundary most recently returned.
getText
public abstract CharacterIterator getText()
- Get the text being scanned
- Returns:
- the text being scanned
setText
public void setText(String newText)
- Set a new text string to be scanned. The current scan
position is reset to first().
- Parameters:
newText - new text to scan.
setText
public abstract void setText(CharacterIterator newText)
- Set a new text for scanning. The current scan
position is reset to first().
- Parameters:
newText - new text to scan.
getWordInstance
public static BreakIterator getWordInstance()
- 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)
- Returns:
- A BreakIterator for word-breaks
- See Also:
Locale.getDefault()
getWordInstance
public static BreakIterator getWordInstance(Locale where)
- 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.
- Returns:
- A BreakIterator for word-breaks
getLineInstance
public static BreakIterator getLineInstance()
- 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.
- Returns:
- A BreakIterator for line-breaks
- See Also:
Locale.getDefault()
getLineInstance
public static BreakIterator getLineInstance(Locale where)
- 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.
- Returns:
- A BreakIterator for line-breaks
getCharacterInstance
public static BreakIterator getCharacterInstance()
- 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.
- Returns:
- A BreakIterator for character-breaks
- See Also:
Locale.getDefault()
getCharacterInstance
public static BreakIterator getCharacterInstance(Locale where)
- 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.
- Returns:
- A BreakIterator for character-breaks
getSentenceInstance
public static BreakIterator getSentenceInstance()
- Create BreakIterator for sentence-breaks using default locale
Returns an instance of a BreakIterator implementing sentence breaks.
- Returns:
- A BreakIterator for sentence-breaks
- See Also:
Locale.getDefault()
getSentenceInstance
public static BreakIterator getSentenceInstance(Locale where)
- Create BreakIterator for sentence-breaks using specified locale
Returns an instance of a BreakIterator implementing sentence breaks.
- Parameters:
where - the local. If a specific SentenceBreak is not
avaliable for the specified local, a default SentenceBreak is returned.
- Returns:
- A BreakIterator for sentence-breaks
getAvailableLocales
public static Locale[] getAvailableLocales()
- Returns an array of all locales for which the
get*Instance methods of this class can return
localized instances.
The array returned must contain at least a Locale
instance equal to Locale.US .
- Returns:
- An array of locales for which localized
BreakIterator instances are available.
getLong
protected static long getLong(byte[] buf,
int offset)
getInt
protected static int getInt(byte[] buf,
int offset)
getShort
protected static short getShort(byte[] buf,
int offset)
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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