Question

I currently have have a HashSet of NElement objects. Each NElement object has a unique Element field, and an integer n.

Here are 2 operations I need to do with the data:

1. Iterate over all the values in collection.
2. With Element e, search the collection for an instance of NElement that has e and process it.

Here’s an example of #2:

public void Add(NElement ne) {
    foreach(NElement ne2 in elements) { //elements is the HashSet
        if(ne2.element == ne.element) {
            ne2.Number += ne.Number; //Number is the integer
            return;
        }
    }
    elements.Add(ne);
}

I think there is a better way to accomplish this using a collection other than a List or Set. Any suggestions?

Answer 1

A possible solution would be a bit of a different design. A molecular formula consists of a bunch of elements along with how many of those elements there are. So a possible solution is to have a MolecularFormula class that wraps this information, which is based in a
Map<Element, int>.

A possible example:

public class MolecularFormula
{
    private Map<Element, int> elements = new HashMap<Element, int>();

    //... Constructors etc
    //A list to iterate through all values
    public List<NElement> getElements()
    {
        List<NElement> retList = new ArrayList<NElement>();
        foreach(Element e : elements)
        {
            retList.put(new NElement(e, elements.get(e));
        }
        return retList;
    }

    //To add something
    public void add(Element e, int num)
    {
        if(elements.containsKey(e))
        {
            int newNum = elements.get(e) + num;
            elements.remove(e);
            elements.put(e, newNum);
        }
        else
        {
            elements.put(e, num);
        }
    }
}

This is hastily thrown together and not very efficient at all, but it should give you an idea of a possible option.