BreakIterator

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## 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.charAt(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()` Get the set of Locales for which BreakIterators are installed
`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.
`static BreakIterator` | `getLineInstance()` Create BreakIterator for line-breaks using default locale.
`static BreakIterator` | `getLineInstance(Locale where)` Create BreakIterator for line-breaks using specified locale.
`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.
`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.

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### 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

Method Detail

### clone

    public Object clone()

  Create a copy of this iterator

  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()

  Get the set of Locales for which BreakIterators are installed

  Returns:
    available locales

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