Question

The following method calculates cost. It access other classes when required. Cloud class holds the information for pricing.

However the method is giving me a nullpointer exception at the following line.
BoundaryPrice btp = cloud.getBoundaryPriceMap().get(boundaryType);
The value for totalcost never changes.
Any idea to high light the problem here?

private float getCostForConnector(Connector connector)
{
    Cloud cloud = new Cloud("http://amazon.com/europeEC2Clouds#dublinEC2Cloud", dynDesInventory);
    List<Port> portList = getListOfPort(connector);
    Resource root = findCommonRoot(connector);

    Port p1 = portList.get(0);
    Port p2 = portList.get(1);
    float totalCost = 0.0f;
    try
    {
    String rootBoundaryType = getRootBoundaryType();

    Float dataProducedFromP1 = getDataCountForPort(p1);
    Float dataProducedFromP2 = getDataCountForPort(p2);

    List<String> portOnePathOut =  getListOfNetworkBoundary(p1, root);
    List<String> portTwoPathOut =  getListOfNetworkBoundary(p2, root);

        for(String boundaryType: portOnePathOut)
        {
            BoundaryPrice btp = cloud.getBoundaryPriceMap().get(boundaryType);
            if (btp != null)
            {
                totalCost += btp.getOutPrice(boundaryType) + dataProducedFromP1;
                totalCost += btp.getInPrice(boundaryType) + dataProducedFromP2;
            }
        }

        for(String boundaryType: portTwoPathOut)
        {
            BoundaryPrice btp = cloud.getBoundaryPriceMap().get(boundaryType);
            if (btp != null)
            {
                totalCost += btp.getOutPrice(boundaryType) + dataProducedFromP2;
                totalCost += btp.getInPrice(boundaryType) + dataProducedFromP1;
            }
        }

        BoundaryPrice btp = cloud.getBoundaryPriceMap().get(rootBoundaryType);
        if (btp != null)
        {
            totalCost += (dataProducedFromP1 + dataProducedFromP2) * btp.getIntraPrice(rootBoundaryType);
        }


    }catch(NullPointerException e) {
        System.err.println("Caught NullPointerException: ");
    }
    return totalCost;

}

Answer 1

1. One of portOnePathOut and portTwoPathOut lists is null
2. portList is null
3. cloud.getBoundaryPriceMap() is null
4. btp.getIntraPrice(rootBoundaryType) is numeric wrapper and it is null
5. dataProducedFromP1 or dataProducedFromP2 are null
6. btp.getOutPrice(boundaryType), btp.getIntraPrice(rootBoundaryType) or btp.getInPrice(boundaryType) are null
7. some object inside functions you invoke is null

The list would be much shorter next time when you post the stack trace.