Let's demonstrate the AutoCompleteTextView:
So, You can add AutoCompleteTextview in your activity layout as:

android:layout_height="wrap_content"

android:layout_below="@id/hello"

android:ems="10"

android:hint="auto complete textview"

android:layout_marginTop="8dp"

android:id="@+id/autocomplete"/>

and finally, your activity.java file can be as:

public class MainActivity extends AppCompatActivity {
    AutoCompleteTextView text;
    String[] languages={"android", "java","IOS","JDBC","C#","C++","C"};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        text=(AutoCompleteTextView) findViewById(R.id.autocomplete);
        ArrayAdapter adapter=new ArrayAdapter(this, android.R.layout.simple_list_item_1,languages);
        text.setAdapter(adapter);
        text.setThreshold(1);
    }
}

 You can watch video demo here: