How to create a Face Detection Android App using Machine Learning KIT on Firebase

import android.app.Application;
import com.google.firebase.FirebaseApp;

public class LCOFaceDetection extends Application {
    public final static String RESULT_TEXT = "RESULT_TEXT";
    public final static String RESULT_DIALOG = "RESULT_DIALOG";

    // initializing our firebase
    @Override
    public void onCreate()
    {
        super.onCreate();
        FirebaseApp.initializeApp(this);
    }
}

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.DialogFragment;

public class ResultDialog extends DialogFragment {
    Button okBtn;
    TextView resultTextView;

    @Nullable
    @Override
    public View
    onCreateView(@NonNull LayoutInflater inflater,
                 @Nullable ViewGroup container,
                 @Nullable Bundle savedInstanceState)
    {

        // importing View so as to inflate
        // the layout of our result dialog
        // using layout inflater.
        View view = inflater.inflate(
            R.layout.fragment_resultdialog, container,
            false);
        String resultText = "";

        // finding the elements by their id's.
        okBtn = view.findViewById(R.id.result_ok_button);
        resultTextView
            = view.findViewById(R.id.result_text_view);

        // To get the result text
        // after final face detection
        // and append it to the text view.
        Bundle bundle = getArguments();
        resultText = bundle.getString(
            LCOFaceDetection.RESULT_TEXT);
        resultTextView.setText(resultText);

        // Onclick listener so as
        // to make a dismissable button
        okBtn.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v)
                {
                    dismiss();
                }
            });
        return view;
    }
}

/*package whatever do not write package name here*/

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.DialogFragment;
import android.content.Intent;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.FirebaseApp;
import com.google.firebase.ml.vision.FirebaseVision;
import com.google.firebase.ml.vision.common.FirebaseVisionImage;
import com.google.firebase.ml.vision.common.FirebaseVisionPoint;
import com.google.firebase.ml.vision.face.FirebaseVisionFace;
import com.google.firebase.ml.vision.face.FirebaseVisionFaceDetector;
import com.google.firebase.ml.vision.face.FirebaseVisionFaceDetectorOptions;
import com.google.firebase.ml.vision.face.FirebaseVisionFaceLandmark;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    Button cameraButton;

    // whenever we request for our customized permission, we
    // need to declare an integer and initialize it to some
    // value .
    private final static int REQUEST_IMAGE_CAPTURE = 124;
    FirebaseVisionImage image;
    FirebaseVisionFaceDetector detector;

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

        // initializing our firebase in main activity
        FirebaseApp.initializeApp(this);

        // finding the elements by their id's allotted.
        cameraButton = findViewById(R.id.camera_button);

        // setting an onclick listener to the button so as
        // to request image capture using camera
        cameraButton.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v)
                {

                    // making a new intent for opening camera
                    Intent intent = new Intent(
                        MediaStore.ACTION_IMAGE_CAPTURE);
                    if (intent.resolveActivity(
                            getPackageManager())
                        != null) {
                        startActivityForResult(
                            intent, REQUEST_IMAGE_CAPTURE);
                    }
                    else {
                        // if the image is not captured, set
                        // a toast to display an error image.
                        Toast
                            .makeText(
                                MainActivity.this,
                                "Something went wrong",
                                Toast.LENGTH_SHORT)
                            .show();
                    }
                }
            });
    }

    @Override
    protected void onActivityResult(int requestCode,
                                    int resultCode,
                                    @Nullable Intent data)
    {
        // after the image is captured, ML Kit provides an
        // easy way to detect faces from variety of image
        // types like Bitmap

        super.onActivityResult(requestCode, resultCode,
                               data);
        if (requestCode == REQUEST_IMAGE_CAPTURE
            && resultCode == RESULT_OK) {
            Bundle extra = data.getExtras();
            Bitmap bitmap = (Bitmap)extra.get("data");
            detectFace(bitmap);
        }
    }

    // If you want to configure your face detection model
    // according to your needs, you can do that with a
    // FirebaseVisionFaceDetectorOptions object.
    private void detectFace(Bitmap bitmap)
    {
        FirebaseVisionFaceDetectorOptions options
            = new FirebaseVisionFaceDetectorOptions
                  .Builder()
                  .setModeType(
                      FirebaseVisionFaceDetectorOptions
                          .ACCURATE_MODE)
                  .setLandmarkType(
                      FirebaseVisionFaceDetectorOptions
                          .ALL_LANDMARKS)
                  .setClassificationType(
                      FirebaseVisionFaceDetectorOptions
                          .ALL_CLASSIFICATIONS)
                  .build();

        // we need to create a FirebaseVisionImage object
        // from the above mentioned image types(bitmap in
        // this case) and pass it to the model.
        try {
            image = FirebaseVisionImage.fromBitmap(bitmap);
            detector = FirebaseVision.getInstance()
                           .getVisionFaceDetector(options);
        }
        catch (Exception e) {
            e.printStackTrace();
        }

        // It’s time to prepare our Face Detection model.
        detector.detectInImage(image)
            .addOnSuccessListener(new OnSuccessListener<List<FirebaseVisionFace> >() {
                @Override
                // adding an onSuccess Listener, i.e, in case
                // our image is successfully detected, it will
                // append it's attribute to the result
                // textview in result dialog box.
                public void onSuccess(
                    List<FirebaseVisionFace>
                        firebaseVisionFaces)
                {
                    String resultText = "";
                    int i = 1;
                    for (FirebaseVisionFace face :
                         firebaseVisionFaces) {
                        resultText
                            = resultText
                                  .concat("\nFACE NUMBER. "
                                          + i + ": ")
                                  .concat(
                                      "\nSmile: "
                                      + face.getSmilingProbability()
                                            * 100
                                      + "%")
                                  .concat(
                                      "\nleft eye open: "
                                      + face.getLeftEyeOpenProbability()
                                            * 100
                                      + "%")
                                  .concat(
                                      "\nright eye open "
                                      + face.getRightEyeOpenProbability()
                                            * 100
                                      + "%");
                        i++;
                    }

                    // if no face is detected, give a toast
                    // message.
                    if (firebaseVisionFaces.size() == 0) {
                        Toast
                            .makeText(MainActivity.this,
                                      "NO FACE DETECT",
                                      Toast.LENGTH_SHORT)
                            .show();
                    }
                    else {
                        Bundle bundle = new Bundle();
                        bundle.putString(
                            LCOFaceDetection.RESULT_TEXT,
                            resultText);
                        DialogFragment resultDialog
                            = new ResultDialog();
                        resultDialog.setArguments(bundle);
                        resultDialog.setCancelable(true);
                        resultDialog.show(
                            getSupportFragmentManager(),
                            LCOFaceDetection.RESULT_DIALOG);
                    }
                }
            }) // adding an onfailure listener as well if
            // something goes wrong.
            .addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e)
                {
                    Toast
                        .makeText(
                            MainActivity.this,
                            "Oops, Something went wrong",
                            Toast.LENGTH_SHORT)
                        .show();
                }
            });
    }
}