import android.os.Bundle;
import android.widget.Toast;

import androidx.fragment.app.FragmentActivity;

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.maps.android.SphericalUtil;

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;

    // below are the latitude and longitude 
    // of 2 different locations.
    LatLng sydney = new LatLng(-34, 151);
    LatLng Brisbane = new LatLng(-27.470125, 153.021072);
    Double distance;

    @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;
        // on below line we are calculating the distance between sydney and brisbane
        distance = SphericalUtil.computeDistanceBetween(sydney, Brisbane);

        // in below line we are displaying a toast 
        // message with distance between two locations.
        // in our distance we are dividing it by 1000 to
        // make in km and formatting it to only 2 decimal places.
        Toast.makeText(this, "Distance between Sydney and Brisbane is \n " + String.format("%.2f", distance / 1000) + "km", Toast.LENGTH_SHORT).show();
    }
}