protected final boolean advance() {
    checkState(!successorIterator.hasNext());
    if (!nodeIterator.hasNext()) {
      return false;
    }
    node = nodeIterator.next();
    successorIterator = graph.successors(node).iterator();
    return true;
  }
protected final boolean advance() {
    checkState(!successorIterator.hasNext());
    if (!nodeIterator.hasNext()) {
      return false;
    }
    node = nodeIterator.next();
    successorIterator = graph.successors(node).iterator();
    return true;
  }
protected final boolean advance ( ) { checkState ( ! successorIterator . hasNext ( ) ) ; if ( ! nodeIterator . hasNext ( ) ) { return false ; } node = nodeIterator . next ( ) ; successorIterator = graph . successors ( node ) . iterator ( ) ; return true ; }
Called after {@link #successorIterator} is exhausted. Advances {@link #node} to the next node
and updates {@link #successorIterator} to iterate through the successors of {@link #node}.
Called after {