CDActivity2.java

public class MainActivity extends AppCompatActivity {

    ChatAdapter chatAdapter;
    RecyclerView recyclerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        recyclerView = findViewById(R.id.recyclerView);
        chatAdapter = new ChatAdapter(this);
        recyclerView.setAdapter(chatAdapter);

    }
    
    @Override
    protected void onStop() {
        super.onStop();
       
        chatAdapter = null;
    }
}