The Java TM Tutorial

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Trail: Internationalization
Lesson: Working with Text

## Character Boundaries

> You need to locate character boundaries if your application allows the end user to highlight individual characters or to move a cursor through text one character at a time. To create a `BreakIterator` that locates character boundaries, you invoke the `getCharacterInstance` method, as follows:

> >     BreakIterator characterIterator =
> >              BreakIterator.getCharacterInstance(currentLocale);

> This type of `BreakIterator` detects boundaries between user characters, not just Unicode characters.

> A user character may be composed of more than one Unicode character. For example, the user character ü can be composed by combining the Unicode characters \u0075 (u) and \u00a8 (¨). This isn't the best example, however, because the character ü may also be represented by the single Unicode character \u00fc. We'll draw on the Arabic language for a more realistic example.

> In Arabic the word for house is:

> This word contains three user characters, but it is composed of the following six Unicode characters:

> >     String house = "\u0628" + "\u064e" + "\u064a" +
> >     	       "\u0652" + "\u067a" + "\u064f";

> The Unicode characters at positions 1, 3, and 5 in the `house` string are diacritics. Arabic requires diacritics because they can alter the meanings of words. The diacritics in the example are nonspacing characters, since they appear above the base characters. In an Arabic word processor you cannot move the cursor on the screen once for every Unicode character in the string. Instead you must move it once for every user character, which may be composed by more than one Unicode character. Therefore you must use a `BreakIterator` to scan the user characters in the string.

> The sample program `BreakIteratorDemo`, creates a `BreakIterator` to scan Arabic characters. The program passes this `BreakIterator`, along with the `String` object created previously, to a method named `listPositions`:

> >     BreakIterator arCharIterator =
> >     		BreakIterator.getCharacterInstance(new Locale ("ar","SA"));

> >     listPositions (house, arCharIterator);

> The `listPositions` method uses a `BreakIterator` to locate the character boundaries in the string. Note that the `BreakIteratorDemo` assigns a particular string to the `BreakIterator` with the `setText` method. The program retrieves the first character boundary with the `first` method and then invokes the `next` method until the constant `BreakIterator.DONE` is returned. The code for this routine is as follows:

> >     static void listPositions(String target, BreakIterator iterator) {

> >         iterator.setText(target);
> >         int boundary = iterator.first();

> >         while (boundary != BreakIterator.DONE) {
> >             System.out.println (boundary);
> >             boundary = iterator.next();
> >         }
> >     }

> The `listPositions` method prints out the following boundary positions for the user characters in the string `house`. Note that the positions of the diacritics (1, 3, 5) are not listed:

> >     0
> >     2
> >     4
> >     6

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