'java.lang.ClassCastException: Resource cannot be cast to java.lang.Comparable'

Question

I have a connector which has two ports. Two ports have a common root as Resource. I am trying to find that common root for those two ports.

I need a set of elements for one port(p1) which can be found via getParent method. For the other port (p2) I need to check if any of p2's element does exist in the set. Although I need this method to return an object of type Resource, I am bit stuck at this point. I am getting the following error.

Unexpected problem while loading: 'java.lang.ClassCastException: policy.vddl.model.Resource cannot be cast to java.lang.Comparable' java.lang.ClassCastException: vddl.model.Resource cannot be cast to java.lang.Comparable at java.util.TreeMap.compare(Unknown Source) at java.util.TreeMap.put(Unknown Source) at java.util.TreeSet.add(Unknown Source) at vddl.product.Product.findCommonRoot(Product.java:357)

private Element findCommonRoot(Connector connector)
{

    List<Port> portList = getListOfPort(connector);
    Port p1 = portList.get(0);
    Set<Element> portElementSet = new TreeSet<Element>();

    Element pathElement = p1.getParent();
    while (pathElement != null)
    {
        portElementSet.add(pathElement);
        pathElement = pathElement.getParent();
    }

    Port p2 = portList.get(1);
    Element pathElement2 = p2.getParent();

    for(Element e: portElementSet)
    {
        if(portElementSet.contains(pathElement2))
            pathElement2 = e;
    }

    return pathElement2;
}

Answer 1

Use HashSet instead TreeSet if don't need the elements to be sorted. HashSet is not sorted and doesn't need the elements to be comparable.