Country demo

MainActivity.java

package com.anta40.app.countrycruddemo;

import androidx.annotation.MainThread;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    Button btnAddCountry;
    Button btnSave;
    EditText edtName, edtPopulation;
    RecyclerView rvCountry;
    CountryAdapter countryAdapter;
    SQLiteDBHandler dbHandler;
    List<Country> countries;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbHandler = new SQLiteDBHandler(getApplicationContext());
        countries = dbHandler.getAllCountries();

        rvCountry = (RecyclerView) findViewById(R.id.rvCountry);
        rvCountry.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
        countryAdapter = new CountryAdapter(countries);
        rvCountry.setAdapter(countryAdapter);

        btnAddCountry = (Button) findViewById(R.id.btnAddCountry);

        btnAddCountry.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                LayoutInflater inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
                View popupView = inflater.inflate(R.layout.dialog_input_country, null);
                AlertDialog.Builder adBuilder = new AlertDialog.Builder(MainActivity.this);
                adBuilder.setView(popupView);

                btnSave = (Button) popupView.findViewById(R.id.btnSave);
                edtName = (EditText) popupView.findViewById(R.id.edtName);
                edtPopulation = (EditText) popupView.findViewById(R.id.edtPopulation);

                AlertDialog dialog = adBuilder.create();
                dialog.setCancelable(true);
                dialog.show();

                btnSave.setOnClickListener(new View.OnClickListener()  {
                    @Override
                    public void onClick(View view){
                        Country newCountry = new Country(0, edtName.getText().toString(),
                                Integer.parseInt(edtPopulation.getText().toString()));
                        dbHandler.addCountry(newCountry);
                        dialog.dismiss();

                        countries = dbHandler.getAllCountries();
                        countryAdapter.updateAndRefreshData(countries);
                    }
                });

            }
        });
    }
}