public class RoundedDialog {

    private Activity activity;
    private Context c;
    private TextView titleTextView;
    private TextView msgTextView;
    private Button btn;
    private int theme;
    private int layout;
    private String dialogTitle;
    private String dialogMsg;


    public RoundedDialog(Context context, Activity activity , int themeID, int layoutID, TextView titleTextView, TextView msgTextView, Button button, String title, String message) {
        c = context;
        this. activity = activity;
        theme = themeID;
        layout = layoutID;
        this.titleTextView = titleTextView;
        this.msgTextView = msgTextView;
        btn = button;
        dialogTitle = title;
        dialogMsg = message;
    }

    /**
     * Generates a dialog based on the parameters of the class.
     * Don't forget to call .show()
     * @return A custom AlertDialog
     **/
    public AlertDialog generateDialog() {
        final AlertDialog.Builder builder = new AlertDialog.Builder(c,theme);
        ViewGroup viewGroup = activity.findViewById(android.R.id.content);
        View dialogView = LayoutInflater.from(c).inflate(layout,viewGroup,false);
        titleTextView.setText(dialogTitle);
        msgTextView.setText(dialogMsg);
        builder.setView(dialogView);
        final AlertDialog alertDialog = builder.create();
        btn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                alertDialog.dismiss();
            }
        });
        return alertDialog;
    }
}

public class MainActivity extends AppCompatActivity {

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

        BottomNavigationView navbar = findViewById(R.id.bottom_nav_bar);
        navbar.setSelectedItemId(R.id.home);

        navbar.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch(item.getItemId()) {
                    case R.id.culture:
                        Toasty.info(getApplicationContext(),"Culture selected!", Toast.LENGTH_SHORT,true).show();
                        break;
                    case R.id.beaches:
                        Toasty.info(getApplicationContext(),"Beaches selected!", Toast.LENGTH_SHORT,true).show();
                        break;
                    case R.id.home:
                        Toasty.info(getApplicationContext(),"Home selected!", Toast.LENGTH_SHORT,true).show();
                        break;
                    case R.id.poi:
                        Toasty.info(getApplicationContext(),"POI selected!", Toast.LENGTH_SHORT,true).show();
                        break;
                    default:

                }

                return true;
            }
        });

        TextView dialogTitle = findViewById(R.id.title);
        TextView dialogMessage = findViewById(R.id.msg);
        Button button = findViewById(R.id.buttonOK);
        RoundedDialog roundedDialog = new RoundedDialog(this,this,R.style.RoundedDialog,R.layout.test,dialogTitle,dialogMessage,button,"Title","Message");
        roundedDialog.generateDialog().show();
    }
}