Java Code Examples for java8.util.Optional#empty()

static Optional<Field> toField(ElementNestedObject em) {
  Field.Builder field = Field.newBuilder();
  switch (toEnum(Field.Type.class, em.getType())) {
    case TEXT:
      field.setType(Type.TEXT);
      break;
    case MULTIPLE_CHOICE:
      field.setType(Type.MULTIPLE_CHOICE);
      field.setMultipleChoice(MultipleChoiceConverter.toMultipleChoice(em));
      break;
    case PHOTO:
      field.setType(Type.PHOTO);
      break;
    default:
      return Optional.empty();
  }
  field.setRequired(em.getRequired() != null && em.getRequired());
  field.setId(em.getId());
  field.setLabel(getLocalizedMessage(em.getLabels()));
  return Optional.of(field.build());
}
 

private void elseUse() {
    Student student = new Student("lucy", 18);

    // 创建一个 为 Null 的 Optional
    Optional optional = Optional.empty();

    if (optional.isEmpty()) {
        System.out.println("optional is empty");
    }


    Optional<Student> studentOptional = Optional.ofNullable(student);
    // isPresent() 可以判断当前 Optional 是否为 Null
    if (studentOptional.isPresent()) {
        System.out.println("student is present");
    }
}
 

static Optional<Response> toResponse(Object obj) {
  if (obj instanceof String) {
    return TextResponse.fromString((String) obj);
  } else if (obj instanceof JSONArray) {
    return MultipleChoiceResponse.fromList(toList((JSONArray) obj));
  } else {
    Timber.e("Error parsing JSON in db of " + obj.getClass() + ": " + obj);
    return Optional.empty();
  }
}
 

public Optional<Integer> getIndex(String code) {
  for (int i = 0; i < getOptions().size(); i++) {
    if (getOptions().get(i).getCode().equals(code)) {
      return Optional.of(i);
    }
  }
  return Optional.empty();
}
 

private Optional<ILogicMovable> removeMovableThatCanMoveTo(List<ILogicMovable> movables, int x, int y) {
	for (Iterator<ILogicMovable> iterator = movables.iterator(); iterator.hasNext(); ) {
		ILogicMovable movable = iterator.next();
		if (canMoveTo(movable, x, y)) {
			iterator.remove();
			return Optional.of(movable);
		}
	}
	return Optional.empty();
}
 

public static Optional<Response> fromList(List<String> codes) {
  if (codes.isEmpty()) {
    return Optional.empty();
  } else {
    return Optional.of(new MultipleChoiceResponse(codes));
  }
}
 

@Override
public Optional<_Presence> getPresence() {
    URL path = getClientPath("presence", mxId.getId(), "status");

    MatrixHttpRequest request = new MatrixHttpRequest(new Request.Builder().get().url(path));
    request.addIgnoredErrorCode(404);
    String body = execute(request);
    if (StringUtils.isBlank(body)) {
        return Optional.empty();
    }

    return Optional.of(new Presence(GsonUtil.parseObj(body)));
}
 

private Optional<Response> getSelectedValue(Field field, List<Option> options) {
  if (checkedItem >= 0) {
    return Optional.of(
        new MultipleChoiceResponse(ImmutableList.of(options.get(checkedItem).getCode())));
  } else {
    return Optional.empty();
  }
}
 

@Test(expectedExceptions=ObscureException.class)
public void testEmptyOrElseThrow() throws Exception {
    Optional<Boolean> empty = Optional.empty();

    Boolean got = empty.orElseThrow(new Supplier<ObscureException>() {
        @Override
        public ObscureException get() {
            return new ObscureException();
        }
    });
}
 

public static Optional<JsonObject> findObj(JsonObject o, String key) {
    if (!o.has(key)) {
        return Optional.empty();
    }

    return Optional.ofNullable(o.getAsJsonObject(key));
}
 

@Override
public Optional<JsonObject> getState(String type) {
    URL path = getClientPath("rooms", getAddress(), "state", type);

    MatrixHttpRequest request = new MatrixHttpRequest(new Request.Builder().get().url(path));
    request.addIgnoredErrorCode(404);
    String body = executeAuthenticated(request);
    if (StringUtils.isBlank(body)) {
        return Optional.empty();
    }

    return Optional.of(GsonUtil.parseObj(body));
}
 

@Override
public Optional<JsonObject> getState(String type, String key) {
    URL path = getClientPath("rooms", roomId, "state", type, key);

    MatrixHttpRequest request = new MatrixHttpRequest(new Request.Builder().get().url(path));
    request.addIgnoredErrorCode(404);
    String body = executeAuthenticated(request);
    if (StringUtils.isBlank(body)) {
        return Optional.empty();
    }

    return Optional.of(GsonUtil.parseObj(body));
}
 

@Override
public Optional<MaterialTypeWithCount> tryToTakeMaterial(int maxAmount) {
	if (!isTargetSet() || getPriority() == EPriority.STOPPED) { // if no target is set, or work is stopped don't give materials
		return Optional.empty();
	}

	List<? extends IRequestStack> potentialStacks = stream(getStacks()).filter(IRequestStack::hasMaterial).collect(Collectors.toList());

	if (potentialStacks.isEmpty()) {
		return Optional.empty();
	}

	EMaterialType resultMaterialType = potentialStacks.get(0).getMaterialType();
	int resultCount = 0;

	for (IRequestStack stack : potentialStacks) {
		if (stack.getMaterialType() != resultMaterialType) {
			continue;
		}

		while (resultCount < maxAmount && stack.pop()) {
			resultCount++;
		}

		if (resultCount >= maxAmount) {
			break;
		}
	}

	return Optional.of(new MaterialTypeWithCount(resultMaterialType, resultCount));
}
 

@Override
public Optional<MatrixErrorInfo> tryLeave() {
    try {
        leave();
        return Optional.empty();
    } catch (MatrixClientRequestException e) {
        return e.getError();
    }
}
 

@Test(expectedExceptions=NullPointerException.class)
public void testEmptyOrElseThrowNull() throws Throwable {
    Optional<Boolean> empty = Optional.empty();

    Boolean got = empty.orElseThrow(null);
}
 

@NonNull
public static <T> Optional<T> getValue(LiveData<Loadable<T>> liveData) {
  return liveData.getValue() == null ? Optional.empty() : liveData.getValue().value();
}
 

private Optional<String> validate(Field field, Optional<Response> response) {
  if (field.isRequired() && (response == null || response.isEmpty())) {
    return Optional.of(resources.getString(R.string.required_field));
  }
  return Optional.empty();
}
 

@Test(expectedExceptions=NoSuchElementException.class)
public void testEmptyGet() {
    Optional<Boolean> empty = Optional.empty();

    Boolean got = empty.get();
}
 

public static Optional<Response> fromString(String text) {
  return text.isEmpty() ? Optional.empty() : Optional.of(new TextResponse(text));
}
 

public Optional<String> getId() {
  String s = json.optString(ID_KEY);
  return s.isEmpty() ? Optional.empty() : Optional.of(s);
}