Camera.java

import static android.Manifest.permission.CAMERA;

public class Camera extends AppCompatActivity {

    private static final int PERMISSION_REQUEST_CODE = 101;

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

        if (!checkPermission()) {
            requestPermissionDialog();
        } else {
            openCamera();
        }
    }

  //shouldShowRequestPermissionRationale method helps to determin that user had selected "Never ask again"
    private void requestPermissionDialog() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && !shouldShowRequestPermissionRationale(CAMERA)) {
            openSettingsDialog();
        } else {
            showAlertDialog("Attention",
                    "This app requires camera permission to take photos and videos",
                    "Continue", "Not Now", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {
                            requestPermission();
                        }
                    }, new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {
                            finish();
                        }
                    });
        }
    }

    private void requestPermission() {
        ActivityCompat.requestPermissions(this, new String[]{CAMERA}, PERMISSION_REQUEST_CODE);
    }

    private void showAlertDialog(String title, String message, String positiveButtonText, String negativeButtonText, DialogInterface.OnClickListener positiveListener, DialogInterface.OnClickListener negativeListener) {
        AlertDialog dialog = new AlertDialog.Builder(CameraPermission.this)
                .setPositiveButton(positiveButtonText, positiveListener)
                .setNegativeButton(negativeButtonText, negativeListener)
                .create();
        if (title != null || !title.isEmpty()) {
            dialog.setTitle(title);
        }
        dialog.setMessage(message);
        dialog.show();
    }

    private boolean checkPermission() {
        return ContextCompat.checkSelfPermission(getApplicationContext(), CAMERA) == PackageManager.PERMISSION_GRANTED;
    }

    private void openCamera() {
        //logic for showing camera.
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        if (requestCode == PERMISSION_REQUEST_CODE) {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                openCamera();
            } else {
                finish();
            }
        }
    }

    private void openSettings() {
        Intent intent = new Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
        Uri uri = Uri.fromParts("package", getPackageName(), null);
        intent.setData(uri);
        startActivity(intent);
    }

    private void openSettingsDialog() {
        showAlertDialog("Attention", "It seems that user has denied camera permissions. Please click on settings and then go to Permissions > Camera and enable it. ", "Settings", "Not Now", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                openSettings();
            }
        }, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                finish();
            }
        });
    }
}