Simple implementation of callback on Android Adapter

activity_main.java

public class Activity extends AppCompatActivity implements MyAdapter.Callback {
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.my_layout);
		
		RecyclerView recycler = findViewById(R.id.recycler_view);
		recycler.setAdapter(new MyAdapter(this));
	}
	
	@Override
	public void onChangePosition(int position) {
		// Here you have access to almost everything from inside your Adapter AND your Activity :D
	}
}

adapter.java

public class MyAdapter extends RecyclerView.Adapter<CustomViewHolder> {
	public interface Callback {
		void onChangePosition(int position);
	}
	
	private MyAdapter.Callback mCallback;
	
	public MyAdapter(MyAdapter.Callback callback) {
		this.mCallback = callback;
	}
	
	public void setCallback(MyAdapter.Callback callback) {
		this.mCallback = callback;
	}
	
    	@Override
	public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
		View v = LayoutInflater.from(parent.getContext())
			.inflate(R.layout.my_view, parent, false);
		return new CustomViewHolder(v);
	}
	
	@Override
	public void onBindViewHolder(ViewHolder holder, int position) {
		this.mCallback.onChangePosition(position);
	}
		
	class CustomViewHolder extends RecyclerView.ViewHolder {
		CustomViewHolder(View view) {
			super(view);
		}
	}
}