* You use the factory methods provided by this class to create * instances of various types of break iterators. In particular, * use {@code getWordInstance}, {@code getLineInstance}, * {@code getSentenceInstance}, and {@code getCharacterInstance} * to create {@code BreakIterator}s that perform * word, line, sentence, and character boundary analysis respectively. * A single {@code 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 {@code 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);
* }
* }
*
*
*
* 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:
*
* {@code
* 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 CharacterIterator
*
*/
public abstract class BreakIterator implements Cloneable
{
/**
* Constructor. BreakIterator is stateless and has no default behavior.
*/
protected BreakIterator()
{
}
/**
* Create a copy of this iterator
* @return A copy of this
*/
@Override
public Object clone()
{
try {
return super.clone();
}
catch (CloneNotSupportedException e) {
throw new InternalError(e);
}
}
/**
* DONE is returned by previous(), next(), next(int), preceding(int)
* and following(int) when either the first or last text boundary has been
* reached.
*/
public static final int DONE = -1;
/**
* Returns the first boundary. The iterator's current position is set
* to the first text boundary.
* @return The character index of the first text boundary.
*/
public abstract int first();
/**
* Returns the last boundary. The iterator's current position is set
* to the last text boundary.
* @return The character index of the last text boundary.
*/
public abstract int last();
/**
* Returns the nth boundary from the current boundary. If either
* the first or last text boundary has been reached, it returns
* {@code 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
* {@code BreakIterator.DONE} and the last text boundary would become the
* new text position.
* @param n which boundary to return. A value of 0
* does nothing. Negative values move to previous boundaries
* and positive values move to later boundaries.
* @return The character index of the nth boundary from the current position
* or {@code BreakIterator.DONE} if either first or last text boundary
* has been reached.
*/
public abstract int next(int n);
/**
* Returns the boundary following the current boundary. If the current boundary
* is the last text boundary, it returns {@code 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.
* @return The character index of the next text boundary or
* {@code BreakIterator.DONE} if the current boundary is the last text
* boundary.
* Equivalent to next(1).
* @see #next(int)
*/
public abstract int next();
/**
* Returns the boundary preceding the current boundary. If the current boundary
* is the first text boundary, it returns {@code 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.
* @return The character index of the previous text boundary or
* {@code BreakIterator.DONE} if the current boundary is the first text
* boundary.
*/
public abstract int previous();
/**
* Returns the first boundary following the specified character offset. If the
* specified offset is equal to the last text boundary, it returns
* {@code 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
* {@code BreakIterator.DONE}.
* @param offset the character offset to begin scanning.
* @return The first boundary after the specified offset or
* {@code 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.
*/
public abstract int following(int offset);
/**
* Returns the last boundary preceding the specified character offset. If the
* specified offset is equal to the first text boundary, it returns
* {@code 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
* {@code BreakIterator.DONE}.
* @param offset the character offset to begin scanning.
* @return The last boundary before the specified offset or
* {@code 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.
* @since 1.2
*/
public int preceding(int offset) {
// NOTE: This implementation is here solely because we can't add new
// abstract methods to an existing class. There is almost ALWAYS a
// better, faster way to do this.
int pos = following(offset);
while (pos >= offset && pos != DONE) {
pos = previous();
}
return pos;
}
/**
* Returns true if the specified character offset is a text boundary.
* @param offset the character offset to check.
* @return {@code true} if "offset" is a boundary position,
* {@code false} otherwise.
* @throws IllegalArgumentException if the specified offset is less than
* the first text boundary or greater than the last text boundary.
* @since 1.2
*/
public boolean isBoundary(int offset) {
// NOTE: This implementation probably is wrong for most situations
// because it fails to take into account the possibility that a
// CharacterIterator passed to setText() may not have a begin offset
// of 0. But since the abstract BreakIterator doesn't have that
// knowledge, it assumes the begin offset is 0. If you subclass
// BreakIterator, copy the SimpleTextBoundary implementation of this
// function into your subclass. [This should have been abstract at
// this level, but it's too late to fix that now.]
if (offset == 0) {
return true;
}
int boundary = following(offset - 1);
if (boundary == DONE) {
throw new IllegalArgumentException();
}
return boundary == offset;
}
/**
* 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
* {@code 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.
* @return The text boundary returned from the above methods, first or last
* text boundary.
* @see #next()
* @see #next(int)
* @see #previous()
* @see #first()
* @see #last()
* @see #following(int)
* @see #preceding(int)
*/
public abstract int current();
/**
* Get the text being scanned
* @return the text being scanned
*/
public abstract CharacterIterator getText();
/**
* Set a new text string to be scanned. The current scan
* position is reset to first().
* @param newText new text to scan.
*/
public void setText(String newText)
{
setText(new StringCharacterIterator(newText));
}
/**
* Set a new text for scanning. The current scan
* position is reset to first().
* @param newText new text to scan.
*/
public abstract void setText(CharacterIterator newText);
private static final int CHARACTER_INDEX = 0;
private static final int WORD_INDEX = 1;
private static final int LINE_INDEX = 2;
private static final int SENTENCE_INDEX = 3;
@SuppressWarnings("unchecked")
private static final SoftReference