How to get selected item from RecyclerView list?

I have created a interface for extending functionality of Recycler View and making possible to listen click on every item of list, but i can't make it to work. Nothing happens when i click on any item. Here is my code:

// METHOD FOR INITIALIZATION OF RECYCLER VIEW
public void initRecyclerView() {
    // SETTING ARRAY FOR CATEGORIES
    final CategoryItem categoryItem[] = { new CategoryItem("Birthday", R.drawable.birthday_image),
                                    new CategoryItem("Anniversary", R.drawable.anniversary_image),
                                    new CategoryItem("Anniversary", R.drawable.anniversary_image),
                                    new CategoryItem("Anniversary", R.drawable.anniversary_image),
                                    new CategoryItem("Anniversary", R.drawable.anniversary_image),
                                    new CategoryItem("Anniversary", R.drawable.anniversary_image),
                                    new CategoryItem("Anniversary", R.drawable.anniversary_image),
                                    new CategoryItem("Anniversary", R.drawable.anniversary_image)};

    // FINDING RECYCLER VIEW IN LAYOUT
    recyclerView = (RecyclerView) findViewById(R.id.list);
    recyclerView.setLayoutManager(new GridLayoutManager(this, 2));

    adapter = new CategoriesListAdapter(categoryItem);
    recyclerView.setAdapter(adapter);

    // SETTING ON CLICK LISTENER ON ADAPTER
    adapter.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void setOnItemClick(View view, int position) {
            String clickedItem = String.valueOf(position);
            if ( clickedItem.equals("Birthday") ) {
                Toast.makeText(MainActivity.this, "Clicked on Birthday!", Toast.LENGTH_SHORT).show();
            }
        }
    });
    recyclerView.setItemAnimator(new DefaultItemAnimator());

}

UPDATE:

adapter

public class CategoriesListAdapter extends RecyclerView.Adapter<CategoriesListAdapter.ViewHolder> {

private CategoryItem[] categoryItems;
private static OnItemClickListener onItemClickListener;

public CategoriesListAdapter(CategoryItem[] categoryItems) {
    this.categoryItems = categoryItems;
}

@Override
public CategoriesListAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemLayoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_row, parent, false);
    ViewHolder viewHolder = new ViewHolder(itemLayoutView);
    return viewHolder;
}


@Override
public void onBindViewHolder(final ViewHolder viewHolder, final int position) {

    viewHolder.txtViewTitle.setText(categoryItems[position].getTitle());
    viewHolder.imgViewIcon.setImageResource(categoryItems[position].getImage());

}

// inner class to hold a reference to each item of RecyclerView
public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    public TextView txtViewTitle;
    public ImageView imgViewIcon;

    public ViewHolder(View itemLayoutView) {
        super(itemLayoutView);
        txtViewTitle = (TextView) itemLayoutView.findViewById(R.id.title);
        imgViewIcon = (ImageView) itemLayoutView.findViewById(R.id.image);
        itemLayoutView.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        onItemClickListener.setOnItemClick(v, getAdapterPosition());
    }
}

public void setOnItemClickListener (final OnItemClickListener onItemClickListener) {
    this.onItemClickListener = onItemClickListener;
}

// Return the size of your itemsData (invoked by the layout manager)
@Override
public int getItemCount() {
    return categoryItems.length;
}

}

INTERFACE:

public interface OnItemClickListener {

public void setOnItemClick(View view, int position);

}

It should display toast message if birthday is selected, but it's not displaying anything. I'm instancing array of class and i don't know how to listen clicked item. The answers there didn't help me solving my problem.