Adapters-App List

 Output:

Activity main xml

 <ListView
        android:id="@+id/listview"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

Main Java

public class MainActivity extends AppCompatActivity {

    ListView listview;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        // 1- AdapterView: ListView

        listview = findViewById(R.id.listview);

        // 2- Data Source: String Array

        String[] countries = {"USA", "Germany", "Saudi Arabia","France"};

        // 3- Adapter: acts as a bridge between the

        //            'data source' and the 'AdapterView'

        ArrayAdapter<String> adapter = new ArrayAdapter<>(

                this,

                android.R.layout.simple_list_item_1,

                countries

        );

        // Link Listview with the Adapter

        listview.setAdapter(adapter);

    }

}