Infinite loop breadth first search

Jaman :

I have tried to implement breadth first search but I believe I get stuck in a infinite for loop and I am not sure why. My method is below:

public ArrayList<T> performBreadthFirstSearchUndirectedNonWeighted(UndirectedNonWeightedGraph<T> graph, T startingVertex){

    if (!graph.containsVertex(startingVertex)) {
        throw new IllegalArgumentException("Vertex doesn't exist.");
    }
    T currentVertex;
    ArrayList<T> traversalOrder = new ArrayList<T>();
    ArrayList<T> visitedVertices = new ArrayList<T>();
    LinkedList<T> queue = new LinkedList<T>(); 

     visitedVertices.add(startingVertex);
     queue.add(startingVertex);

     while (queue.size() != 0) {
         currentVertex = queue.poll();
         traversalOrder.add(currentVertex);

         Iterator<Vertex<T>> i = graph.getNeighbours(currentVertex).iterator(); 

         while (i.hasNext()) { 
             Vertex<T> n = i.next(); 
                if (!visitedVertices.contains(graph.returnVertex(n.getElement()))) { 
                    visitedVertices.add(n.getElement());
                    queue.add(n.getElement()); 
                } 
            } 
     }
    return traversalOrder;
}

Any help is appreciated!

Thank you.

EDIT: Updated code still infinite loop.

Ricola :

Replace the line

if (!visitedVertices.contains(graph.returnVertex(n.getElement())))

by

if (!visitedVertices.contains(n.getElement()))

The method contains accept an Object as a parameter so it compiles fine but you have to give a object of type T. Normally if you are using an IDE, it should warn you on this line.