This shows or hides a floating action button when the recycler view is scrolled. It also adds a blank space after the list's last item to make sure that if the list is too short to be scrolled, it'll still be scrollable to hide the floating action button that is sitting on top of the last item.

addBlankSpaceAfterLastItem.java

// This code is inside the recycler view adapter class
@Override
public void onBindViewHolder(final ViewHolder holder, int position) {
    if (position + 1 == getItemCount()) {
        // It is the last item of the list

        // Set bottom margin to 72dp
        setBottomMargin(holder.itemView, (int) (72 * Resources.getSystem().getDisplayMetrics().density));
    } else {
        // Reset bottom margin back to zero
        setBottomMargin(holder.itemView, 0);
    }
}

/**
 * Sets a margin to the bottom of the view.
 *
 * @param view         The view to add the margin to.
 * @param bottomMargin The bottom margin to be added to the view.
 */
private static void setBottomMargin(View view, int bottomMargin) {
    if (view.getLayoutParams() instanceof ViewGroup.MarginLayoutParams) {
        ViewGroup.MarginLayoutParams params = (ViewGroup.MarginLayoutParams) view.getLayoutParams();
        params.setMargins(params.leftMargin, params.topMargin, params.rightMargin, bottomMargin);
        view.requestLayout();
    }
}

showHideFloatingActionButton.java

recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                if (dy < 0) {
                    // Scrolled up, show floating action button
                    fab.show();
                } else if (dy > 0) {
                    // Scrolled down, hide floating action button
                    fab.hide();
                }
            }
        });