public class Child {

    String name;

    public Child(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

public class SectionHeader implements Section<Child> {

    List<Child> childList;
    String sectionText;

    public SectionHeader(List<Child> childList, String sectionText) {
        this.childList = childList;
        this.sectionText = sectionText;
    }

    @Override
    public List<Child> getChildItems() {
        return childList;
    }

    public String getSectionText() {
        return sectionText;
    }
}

public class SectionViewHolder extends RecyclerView.ViewHolder {

    TextView name;
    public SectionViewHolder(View itemView) {
        super(itemView);
         name = (TextView) itemView.findViewById(R.id.section);
    }
}

public class ChildViewHolder extends RecyclerView.ViewHolder {

    TextView name;
    public ChildViewHolder(View itemView) {
        super(itemView);
        name = (TextView) itemView.findViewById(R.id.child);
    }
}

public class AdapterSectionRecycler extends SectionRecyclerViewAdapter<SectionHeader, Child, SectionViewHolder, ChildViewHolder> {

    Context context;

    public AdapterSectionRecycler(Context context, List<SectionHeader> sectionItemList) {
        super(context, sectionItemList);
        this.context = context;
    }

    @Override
    public SectionViewHolder onCreateSectionViewHolder(ViewGroup sectionViewGroup, int viewType) {
        View view = LayoutInflater.from(context).inflate(R.layout.section_item, sectionViewGroup, false);
        return new SectionViewHolder(view);
    }

    @Override
    public ChildViewHolder onCreateChildViewHolder(ViewGroup childViewGroup, int viewType) {
        View view = LayoutInflater.from(context).inflate(R.layout.item_layout, childViewGroup, false);
        return new ChildViewHolder(view);
    }

    @Override
    public void onBindSectionViewHolder(SectionViewHolder sectionViewHolder, int sectionPosition, SectionHeader section) {
        sectionViewHolder.name.setText(section.sectionText);
    }

    @Override
    public void onBindChildViewHolder(ChildViewHolder childViewHolder, int sectionPosition, int childPosition, Child child) {
        childViewHolder.name.setText(child.getName());
    }
}

public class MainActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    AdapterSectionRecycler adapterRecycler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //initialize RecyclerView
        recyclerView = (RecyclerView) findViewById(R.id.recycler_view);

        //setLayout Manager
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(linearLayoutManager);
        recyclerView.setHasFixedSize(true);

        //Create a List of Child DataModel
        List<Child> childList = new ArrayList<>();
        childList.add(new Child("April"));
        childList.add(new Child("Austin"));
        childList.add(new Child("Alex"));
        childList.add(new Child("Aakash"));

        //Create a List of Section DataModel implements Section
        List<SectionHeader> sections = new ArrayList<>();
        sections.add(new SectionHeader(childList, "A"));

        childList = new ArrayList<>();
        childList.add(new Child("Bill Gates"));
        childList.add(new Child("Bob Proctor"));
        childList.add(new Child("Bryan Tracy"));
        sections.add(new SectionHeader(childList, "B"));

        childList = new ArrayList<>();
        childList.add(new Child("Intruder Shanky"));
        childList.add(new Child("Invincible Vinod"));
        sections.add(new SectionHeader(childList, "I"));

        childList = new ArrayList<>();
        childList.add(new Child("Jim Carry"));
        sections.add(new SectionHeader(childList, "J"));

        childList = new ArrayList<>();
        childList.add(new Child("Neil Patrick Harris"));
        sections.add(new SectionHeader(childList, "N"));

        childList = new ArrayList<>();
        childList.add(new Child("Orange"));
        childList.add(new Child("Olive"));
        sections.add(new SectionHeader(childList, "O"));

        adapterRecycler = new AdapterSectionRecycler(this, sections);
        recyclerView.setAdapter(adapterRecycler);
    }
}

insertNewSection(Section)
insertNewSection(Section, int)
removeSection(int)
insertNewChild(Object, int)
insertNewChild(Object, int, int)
removeChild(int, int)

/* To notify the adapter for data change 
 * call notifyDataChanged(List) instead of 
 * notiftDatasetChanged()
 */ 
notifyDataChanged(List)