It's more simple callback for calculating the diff between two non-null items in a list.

DiffUtilCallback

/**
 * It's more simple callback for calculating the diff between two non-null items in a list.
 * <p>
 * {@link DiffUtil.Callback} serves two roles - list indexing, and item diffing. ItemCallback handles
 * just the second of these, which allows separation of code that indexes into an array or List
 * from the presentation-layer and content specific diffing code.
 *
 * @param <T> Type of items to compare.
 */
public abstract class DiffUtilCallback<T> extends DiffUtil.Callback {

    private List<T> oldItemsList;
    private List<T> newItemsList;

    public final DiffUtil.DiffResult calculateDiff(List<T> oldItems, List<T> newItems, boolean detectMoves) {
        this.oldItemsList = oldItems;
        this.newItemsList = newItems;
        return DiffUtil.calculateDiff(this, detectMoves);
    }

    public final DiffUtil.DiffResult calculateDiff(List<T> oldItems, List<T> newItems) {
        this.oldItemsList = oldItems;
        this.newItemsList = newItems;
        return DiffUtil.calculateDiff(this);
    }

    @Override
    public final int getOldListSize() {
        return oldItemsList.size();
    }

    @Override
    public final int getNewListSize() {
        return newItemsList.size();
    }

    @Override
    public final boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
        return areItemsTheSame(oldItemsList.get(oldItemPosition), newItemsList.get(newItemPosition));
    }

    @Override
    public final boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
        return areContentsTheSame(oldItemsList.get(oldItemPosition), newItemsList.get(newItemPosition));
    }

    public abstract boolean areItemsTheSame(T oldItem, T newItem);

    public abstract boolean areContentsTheSame(T oldItem, T newItem);

}