What does the dot mean at the end of an associatio

问题:

I reversed some Java code to get a uml class diagram using Visual Paradigm. The diagram shows some associations with little black circles on one end, which I never saw before.

Image

It's definitely not a composition and not a containment! Can anybody explain to me, what kind of association this is?

Here's the related code:

public class DataAdapter extends RecyclerView.Adapter<DataAdapter.ViewHolder> {
    public static final String TAG = DataAdapter.class.getSimpleName();

    private static Context mContext;
    private ArrayList<DataClass> mData;
    private static OnItemClickListener<DataClass> mListener;

    public static class ViewHolder extends RecyclerView.ViewHolder {}

    public DataAdapter(Context context, ArrayList<DataClass> data) {}

    public void setOnClickListener(OnItemClickListener listener) {}

    @Override
    public int getItemCount() {}

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {}

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {}
}

public interface OnItemClickListener<T> {
    public void onItemClick(T item);
}

回答1:

What you are seeing is the ownership indicator, commonly known as the dot
In this case it indicates that the property at right side of the association is owned by the class on the left side.

From the UML specs v2.5:

Ownership of Association ends by an associated Classifier may be indicated graphically by a small filled circle, which for brevity we will term a dot. The dot is to be drawn integral to the graphic path of the line, at the point where it meets the Classifier, inserted between the end of the line and the side of the node representing the Classifier. The diameter of the dot shall not exceed half the height of the aggregation diamond, and shall be larger than the width of the line. This avoids visual confusion with the filled diamond notation while ensuring that it can be distinguished from the line. The dot shows that the model includes a Property of the type represented by the Classifier touched by the dot. This Property is owned by the Classifier at the other end. In such a case it is normal to suppress the Property from the attributes compartment of the owning Classifier.

回答2:

To adorn Geert's correct answer: In former UML versions navigability (an open arrow at either side) was (mis-) used for that purpose. So now that you see a dot it also means you can navigate towards it (because it renders an attribute of the class type it's touching). It is still possible to mix both notations. But it does not make much sense. Personally I'd use (if ever) navigational arrows only in a conceptual phase.