标题翻译
LinkedHashSet returns as HashSet in Low level datastore fetch Java
问题
参数声明如下，
@Persistent private Set<ScopeType> scope = new LinkedHashSet<ScopeType>();
在使用高级数据存储器获取时，它会返回 LinkedHashSet，但在低级别获取时，响应是 HashSet，这是否是预期的行为？
英文翻译
The parameter is declared as follows,
@Persistent private Set<ScopeType> scope = new LinkedHashSet<ScopeType>();
While fetching with High-level datastore fetch, it responds with LinkedHashSet, but on Low-level fetch the response is a HashSet, Is this something expected?
答案1
得分: 0
看起来是合理的。 scope 的类型是 Set，不是 LinkedHashSet 也不是 HashSet。这些是实现类型。scope 的任何用户只保证满足已声明的类型，不能保证使用特定的实现。
如果必须保留 LinkedHashSet 的保持顺序的特性，则必须将 scope 声明为 LinkedHashSet。
在这种情况下，将具体类型用作声明类型会违反大多数样式规则，但是这是不可避免的。没有类似于 Set 的接口可供使用。这是 Java 类型的限制导致的结果。
英文翻译
That looks reasonable. The type of scope is Set, not LinkedHashSet nor HashSet. Those are implementation types. Any user of scope is only guaranteed that the declared type is satisfied, not that a particular implementation is in use.
If the order-preserving feature of LinkedHashSet must be maintained, then scope must be declared as LinkedHashSet.
Using a concrete type as a declared type breaks most style rules, but is in this case unavoidable. There is no interface similar to Set which is available to be used. That is a consequence of limitations of java's typing.
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