为什么 Java 可变参数不支持集合？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/6898653/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Why doesn't Java varargs support collections?
提问by tb189
In my Java code I often use the very handy method(Class... args)varargs. As far as I know, they allow you to pass any amount of Classobjects or an array of Class[]. Since I also often use the Java collection classes, I am frustrated by the lack of compatibility between both. As a result, I end up doing collection.toArray(), but that has some type safety issues.
在我的 Java 代码中，我经常使用非常方便的method(Class... args)可变参数。据我所知，它们允许您传递任意数量的Class对象或Class[]. 由于我也经常使用 Java 集合类，我对两者之间缺乏兼容性感到沮丧。结果，我最终做了collection.toArray()，但这有一些类型安全问题。
So now for the question: why doesn't Java allow instances of Iterable<T>as vararg arguments, as long as the generic type fits the T...type of the vararg? Doesn't everyone use lists, sets, etc. all the time? Is there an easy, type-safe way to provide the conversion from collection to vararg?
那么现在问题来了：Iterable<T>只要泛型类型适合T...vararg的类型，为什么 Java 不允许as vararg 参数的实例？不是每个人都一直使用列表、集合等吗？有没有一种简单的、类型安全的方法来提供从集合到可变参数的转换？
回答by Joachim Sauer
The reason is simple: a variable arity parameter is simply an old-school array paramater with some additional metadata that tells the compiler to provide some syntactic sugar (namely, it allows implicit array creation).
原因很简单：变量 arity 参数只是一个带有一些额外元数据的老式数组参数，它告诉编译器提供一些语法糖（即，它允许隐式数组创建）。
So from the perspective of the JVM Object...is pretty much the same as Object[]. Allowing collections as well would require a more invasive change to the JVM (which has no explicit support for collections to date).
所以从 JVM 的角度来看，Object...与Object[]. 允许集合也需要对 JVM（迄今为止没有明确支持集合）进行更具侵入性的更改。
Note that if you want to support both ways, then making the collection-based method is probably the better approach:
请注意，如果您想同时支持两种方式，那么使用基于集合的方法可能是更好的方法：
public void frobnicate(Object... args) {
frobnicate(Arrays.asList(args));
}
public void frobnicate(Iterable<Object> args) {
// do stuff
}
The reason for this is that using Arrays.asList()is usuallya cheaper operation than Collection.toArray()(because it creates a simple wrapper).
这样做的原因是，使用Arrays.asList()是通常比一个更便宜的操作Collection.toArray()（因为它创建一个简单的包装）。
