What can I store a single element in a Collection? [closed]

Question

I've got a DTO object used to get data from my server. It can be used for one or several elements. This DTO encapsulate a Collection containing the data.

When my DTO brings me only one element, how should I store it?

Sample code:

public class DataDTO implements Serializable
{
    private Collection<Data> data;

    public DataDTO()
    {
    }

    public Collection<Data> getData()
    {
        return data;
    }


    public void setData(Collection<Data> data)
    {
        this.data = data;
    }


    public void setData(Data singleData)
    {
        // At this time I use an ArrayList initialized with a capacity of 1
        this.data = new ArrayList<Data>(1);
        this.data.add(singleData);
    }
}

Answer 1

You can use singleton methods from Collections class.

singletonList : Returns an immutable list containing only the specified object. The returned list is serializable.

singleton : Returns an immutable set containing only the specified object. The returned set is serializable.

singletonMap : Returns an immutable map, mapping only the specified key to the specified value. The returned map is serializable.

Answer 2

The question is, what do you want to do later with it? Is there a chance that you migh add another element? If not, you could use

this.data = Collections.singletonList( singleData );

If there is a chance that you might want to add elements later, then it's the typical question what List implementation to use, ArrayList is fine for many cases.