First of all, let's modify the IDataSource interface, adding to it a method for returning a selected range of celebrities:

public interface IDataSource
{
List<Celebrity> getAllCelebrities();
Celebrity getCelebrityById(long id);
void addCelebrity(Celebrity c);
List<Celebrity> getRange(int indexFrom, int indexTo);
}

Next, we need to implement this method in the available implementation of this interface. Add the following method to the MockDataSource class:

public List<Celebrity> getRange(int indexFrom, int indexTo)
{
List<Celebrity> result = new ArrayList<Celebrity>();
for (int i = indexFrom; i <= indexTo; i++)
{
result.add(celebrities.get(i));
}
return result;
}

The code is quite simple, we are returning a subset of the existing collection starting from one index value and ending with the other. In a real-life implementation, we would probably check whether indexTo is bigger than indexFrom, but here, let's keep things simple.

Here is one...