Структура приложения в Android Studio

package com.sonexrfs.maplocs;
 
import android.support.v4.app.FragmentActivity;
import android.os.Bundle;
 
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import android.view.View;
import android.widget.Button;
 
 
public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {
 
    private GoogleMap mMap;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
 
    }
 
 
    /**
     * Manipulates the map once available.
     * This callback is triggered when the map is ready to be used.
     * This is where we can add markers or lines, add listeners or move the camera. In this case,
     * we just add a marker near Sydney, Australia.
     * If Google Play services is not installed on the device, the user will be prompted to install
     * it inside the SupportMapFragment. This method will only be triggered once the user has
     * installed Google Play services and returned to the app.
     */
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
 
        // Add a marker in Sydney and move the camera
        LatLng sydney = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
 
        //mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(
        //        new LatLng(-18.142, 178.431), 2));
 
        // Other supported types include: MAP_TYPE_NORMAL,
        // MAP_TYPE_TERRAIN, MAP_TYPE_HYBRID and MAP_TYPE_NONE
        mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
    }
 
 
   // Мой метод переключения кнопкой
    int tag_buyton3 = 0;
    public void onButton3Click(View view)
    {
        Button button3 = (Button)findViewById(R.id.button3);
 
        tag_buyton3 = tag_buyton3 + 1;
        if (tag_buyton3 == 1) {
            mMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
            button3.setText("Map 2");
        }
        if (tag_buyton3 == 2) {
            mMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
            button3.setText("Map 3");
        }
        if (tag_buyton3 == 3) {
            mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
            button3.setText("Map 1");
        }
        if (tag_buyton3 == 3) {
            tag_buyton3 = 0;
        }
    }
 
}

public void onButton3Click(View view)