Create simple program which show the use of auto complete text view, using Java in Android Studio.

 Java Code: -

public class MainActivity extends AppCompatActivity {
    AutoCompleteTextView textView;

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

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_dropdown_item_1line, COUNTRIES);

        textView = findViewById(R.id.txt_view);
        textView.setAdapter(adapter);
    }

    private static final String[] COUNTRIES = new String[] {
            "India", "Russia", "Germany"
    };
}

XML Code: -

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <AutoCompleteTextView
        android:id="@+id/txt_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter text here"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="LabelFor" />

</androidx.constraintlayout.widget.ConstraintLayout>