FormActivity.java

@ValidComponent
AutoValidatedTextInputEditText usernameEditText;

@ValidComponent
AutoValidatedTextInputEditText birthdateEditText;

Button submit;
    
/* ...   snip  ... */
final static String userFriendlyBirthdayDateFormat = "MM/dd/yy";
final static SimpleDateFormat userFriendlyBirthdayDateFormatter = new SimpleDateFormat(userFriendlyBirthdayDateFormat);

//Somewhere inside onCreate
usernameEditText = ...
birthdateEditText = ...

usernameEditText.addValidators(UsernameValidator.getInstance());
birthdateEditText.addValidators(new DateValidator(userFriendlyBirthdayDateFormat));

birthdateEditText.setOnClickListener(v -> {
  DatePickerDialog.OnDateSetListener dateSelectedListener = (view, year, monthOfYear, dayOfMonth) -> {
      /* Setup date listener */
  };

  /* Setup date picked callback */
  // When date is picked, set birthdateEditText to have the picked date, as a friendly user format
  };
);

submit = ...

final Calendar currentCalendarInUTC = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
submit.setOnClickListener(v -> {
    ComponentValidator.Response validationResponse = ComponentValidator.getInstance().validate(this);
    if (!validationResponse.isValid()) {
        validationResponse.firstInvalidComponent().requestFocus();
        VirtualKeyboardManager.showVirtualKeyboard(_activity);
        return;
    }
  
  /* Continue with submit logic */
});

private class UsernameValidator implements TextValidator {

    private static final UsernameValidator _instance;

    static {
        _instance = new UsernameValidator();
    }

    private UsernameValidator() {
    }

    public static UsernameValidator getInstance() {
        return _instance;
    }

    @Override
    public String validate(String content) {
        return content.matches("^[a-zA-Z0-9_.]+") ? null : "Usernames should contain alphanumeric characters, underscores & periods only";
    }
}

public class DateValidator implements TextValidator {

    SimpleDateFormat sdf;

    public DateValidator(String format) {
        this.sdf = new SimpleDateFormat(format);
    }

    public DateValidator(SimpleDateFormat sdf) {
        this.sdf = sdf;
    }

    @Override
    public String validate(String content) {
        try {
            sdf.parse(content);
            return null;
        } catch (ParseException e) {
        }
        return "Invalid date format";
    }
}