hasNext()

while

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));
     }
 }

fun printEachForward(boundary: BreakIterator, source: String) {
    var start = boundary.first()
    var end = boundary.next()
    while (end != BreakIterator.DONE) {
        println(source.substring(start, end))
        start = end
        end = boundary.next()
    }
}