init-rv.java

List<Post> posts = ...; // Fill the list with initial data
PostAdapter adapter = new PostAdapter(this, posts); // Initialize the RecyclerView Adapter
recyclerView.setAdapter(adapter); // Set adapter to the RecyclerView

/**
  * Running some operation that modify the `posts` list
 **/

adapter.notifyDataSetChanged; // Notify the adapter that the `posts` list already changed,
                              // it can also substituted with `notifyItemInserted`,
                              // `notifyItemChanged`, `notifyItemRemoved`, etc