为什么 Google Guava 提供存在等效构造函数的静态方法？

Question

我注意到 Google Guava Sets class offers methods such as newHashSet taking an Iterable or Iterator. The HashSet class 与 Java 捆绑在一起已经提供了一个采用 Collection 的构造函数，从而提供了类似的行为。

所以我很好奇……Guava Sets中这些特定的静态方法有什么优势？仅仅是因为 Iterable 或 Iterator 对象 而不是 也是 Collection 吗？或者 Guava 团队是否有其他目的而费心包含这些方法？

Answer 1

根据 Google Guava 文档，CollectionUtilitiesExplained：

Whenever possible, Guava prefers to provide utilities accepting an Iterable rather than a Collection. Here at Google, it's not out of the ordinary to encounter a "collection" that isn't actually stored in main memory, but is being gathered from a database, or from another data center, and can't support operations like size() without actually grabbing all of the elements.

As a result, many of the operations you might expect to see supported for all collections can be found in Iterables. Additionally, most Iterables methods have a corresponding version in Iterators that accepts the raw iterator.

The overwhelming majority of operations in the Iterables class are lazy: they only advance the backing iteration when absolutely necessary. Methods that themselves return Iterables return lazily computed views, rather than explicitly constructing a collection in memory.

Answer 2

Iterable 接口在 Java 1.5 中引入，是 Collection 接口

的基础接口

HashSet 构造函数早于此修改，我认为为了兼容性，他们将其保留为 Java 1.5

另一方面，Guava 不受此更改的限制，为方便起见，提供了采用 Iterator.

的构造函数

默认情况下 Iterable 构造函数尝试将 Iterable 转换为 Collection，如果不可能，则继续提取其 Iterator 并调用 Iterator构造函数。

在我看来，这为图书馆用户提供了更好的灵活性。

存在 Sets 实用程序 class 的另一个原因是 Java 1.5 和 1.6 在调用泛型构造函数时需要手写。

这个特殊问题在 1.7 中通过引入菱形运算符得到解决。

举例说明。

1.7 之前

ArrayList<String> myList = ...
// See generic parameter repeated
HashSet<String> mySet = new HashSet<String>( myList );
// No such issue for statics
HashSet<String> myGuavaSet = Sets.newHashSet( myList );

1.7 之后

ArrayList<String> myList = ...
// Notice diamond
HashSet<String> mySet = new HashSet<>( myList );
// Really no reason now to use Guava for HashSet construction in most cases

为什么 Google Guava 提供存在等效构造函数的静态方法？

Why does Google Guava offer static methods where equivalent constructors exist?

java

constructor

guava