private class AdjacentVerticesIterator implements VertexIterator {
        int nextPos = -1;
        int vertex;
        
        AdjacentVerticesIterator(int v) 
        {
            vertex = v;
            findNext();
        }
        
        private void findNext() 
        {
            nextPos++;
            while (nextPos < numVertices &&
            		!edgeCosts.containsKey(new Edge(vertex, nextPos)))
                nextPos++;
        }

        public boolean hasNext() 
        {
            return nextPos < numVertices;
        }
        
        public int next() 
        {
            int pos = nextPos;
            if (pos < numVertices) {
                findNext();
                return pos;
            }
            
            throw new NoSuchElementException(
                "This iterator has no more elements.");
        }
    }