问题

假设我有以下布局：

```java
public void caller(@NonNull List<Integer> param){
  // param可以是空的，但不能为null，它不可为空
  if(!param.isEmpty()) function(Optional.of(param));
  // 如果param是空的，那就不要调用"function"
}


public void function(Optional<List<Integer>> someParam){
  someParam.ifPresent(...);
}

问题是：基于空列表创建Optional是否是正确的用法？我感到困惑的是，我们是否应该提供一个Optional，无论caller中的param是否为空，因为它不为null，但我想知道这是否是正确的用法？

<details>
<summary>英文:</summary>

Suppose I have this layout:

public void caller(@NonNull List<Integer> param){
// param COULD BE EMPTY, but it CANNOT be NULL, its not nullable
if(!param.isEmpty()) function(Optional.of(param));
// If param is empty then just dont call "function"
}

public void function(Optional<List<Integer>> someParam){
someParam.ifPresent(...);
}

Here is the question: Is not creating an `Optional` based on an empty list correct usage? The confusion I am having is whether we should be providing an Optional regardless if `param` in `caller` is empty or not because it is not null, but I am wondering if this is the right usage?



</details>


# 答案1
**得分**: 3

1. `someParam.ifPresent(...);` `ifPresent` 方法的主体总是会被调用，因为总是会有一个元素，即使它是一个空列表（你正在检查非空性 `@NonNull List&lt;Integer&gt; param`）。
2. 你正在使用 `Optional.of` 而不是 `Optional.ofNullable`，因此始终会有一个非空元素。
3. 将列表包装在 `Optional` 中没有太多意义，为什么不传递一个空列表并且不处理任何元素呢？
4. `if(!param.isEmpty())` 是多余的，因为你知道列表中有元素，就像第3点所述，为什么不直接传递列表进行处理呢？

**简而言之**：你将空列表与 `null` 混淆了，在任何集合中包装 `Optional` 都没有太多意义。

<details>
<summary>英文:</summary>

 1.  `someParam.ifPresent(...);` the body of `ifPresent` is always invoked, because there always is an element, even if it&#39;s an empty list (you&#39;re checking for nullity `@NonNull List&lt;Integer&gt; param`).
 2. You&#39;re using `Optional.of` instead of `Optional.ofNullable`, so there is always going to be a non-null element.
 3. Wrapping list in `Optional` does not make much sense, why not passing an empty list and not processing any elements?
 4. `if(!param.isEmpty())` is redundant, because you know there are elements in the list, as stated in 3. why not passing the list for processing?

**tl;dr**: You&#39;re mixing an empty list with `null`, wrapping any collection in `Optional` does not make much sense. 

</details>