question: private boolean incrementSentence ( ) throws IOException { if ( length == 0 ) return false ; while ( true ) { int start = iterator . current ( ) ; if ( start == BreakIterator . DONE ) return false ; int end = iterator . next ( ) ; if ( end == BreakIterator . DONE ) return false ; setNextSentence ( start , end ) ; if ( incrementWord ( ) ) { return true ; } } }
target:  return true if there is a token from the buffer, or null if it is exhausted.