Since the application will be displaying changes of financial stocks over time, it means that we will be working with data that's represented best as a list. For this, we will use RecyclerView. 

First of all, add it to your activity_main.xml file:

<android.support.v7.widget.RecyclerView
    android:id="@+id/stock_updates_recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/hello_world_salute" />

Then, inject it into your code with the following:

@BindView(R.id.stock_updates_recycler_view)
RecyclerView recyclerView;

The next step is to initialize it in your activity:

private LinearLayoutManager layoutManager;
private StockDataAdapter stockDataAdapter;

...
recyclerView.setHasFixedSize(true);

layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);

stockDataAdapter = new StockDataAdapter();
recyclerView.setAdapter(stockDataAdapter);

The code for the StockDataAdapter is as illustrated:

public class StockDataAdapter extends RecyclerView.Adapter<StockUpdateViewHolder> {
private final List<String> data = new ArrayList<>();

@Override
    public StockUpdateViewHolder onCreateViewHolder(ViewGroup parent, 
      int viewType) {
        View v = LayoutInflater.from(parent.getContext())
          .inflate(R.layout.stock_update_item, parent, false);
        StockUpdateViewHolder vh = new StockUpdateViewHolder(v);
        return vh;
    }

    @Override
    public void onBindViewHolder(StockUpdateViewHolder holder, int 
      position) {
        holder.stockSymbol.setText(data.get(position));
    }

    @Override
    public int getItemCount() {
        return data.size();
    }

    public void add(String stockSymbol) {
        this.data.add(stockSymbol);
        notifyItemInserted(data.size() - 1);
    }
}

Finally, we need the layout XML for the RecyclerView items and a ViewHolder for them:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="3dp">

    <TextView
        android:id="@+id/stock_item_symbol"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_margin="20dp" />
</android.support.v7.widget.CardView>

To fill in the data for this view, we will have to utilize ViewHolders from the RecyclerView class:

public class StockUpdateViewHolder extends RecyclerView.ViewHolder {
@BindView(R.id.stock_item_symbol)
    TextView stockSymbol;

public StockUpdateViewHolder(View v) {
        super(v);
        ButterKnife.bind(this, v);
    }
}

The very last step is to populate it with the data. We will do that in a Reactive way:

Observable.just("APPL", "GOOGLE", "TWTR")
        .subscribe(new Consumer<String>() {
            @Override
            public void accept(String stockSymbol) {
                stockDataAdapter.add(stockSymbol);
            }
        });

This is rather simple code and I hope that most of the developers had no trouble following this. In case there were some not-so-clear bits, feel free to check out the code that's provided with this book. The examples there are fully working.