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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 aBreakIterator
that locates character boundaries, you invoke thegetCharacterInstance
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 aBreakIterator
to scan the user characters in the string.The sample program
BreakIteratorDemo
, creates a
BreakIterator
to scan Arabic characters. The program passes thisBreakIterator
, along with theString
object created previously, to a method namedlistPositions
:BreakIterator arCharIterator = BreakIterator.getCharacterInstance(new Locale ("ar","SA")); listPositions (house, arCharIterator);The
listPositions
method uses aBreakIterator
to locate the character boundaries in the string. Note that theBreakIteratorDemo
assigns a particular string to theBreakIterator
with thesetText
method. The program retrieves the first character boundary with thefirst
method and then invokes thenext
method until the constantBreakIterator.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 stringhouse
. Note that the positions of the diacritics (1, 3, 5) are not listed:0 2 4 6
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