扩展列表< T>在Java 8中 [英] Extending List<T> in Java 8

问题描述

我经常想将一个列表映射到另一个列表。例如，如果我有一个人员列表，我想要一个他们的名字列表，我想这样做：

I often want to map one list into another list. For example if I had a list of people, and I wanted a list of their names, I would like to do:

GOAL

List<Person> people = ... ;

List<String> names = people.map(x -> x.getName());

使用Java 8可以实现这样的目标：

Something like this is possible with Java 8:

JAVA 8版本

List<String> names = people.stream()
                           .map(x -> x.getName())
                           .collect(Collectors.toList());

但这显然不是很好。事实上，我认为使用Guava更清洁：

But this is clearly not as nice. In fact, I think using Guava is cleaner:

GUAVA VERSION

List<String> names = Lists.transform(people, x -> x.getName());

但是，我喜欢链接。那么，我的目标是否可能？

However, I do like chaining. So, is my goal possible?

我听说有人说Java 8默认方法类似于C＃扩展方法。使用C＃扩展方法，我可以轻松地将辅助方法添加到 IEnumerable< T> ：

I have heard people say that Java 8 default methods are similar to C# extension methods. With a C# extension method, I could easily add a helper method to IEnumerable<T>:

public static IEnumerable<TRet> Map<T, TRet>(this IEnumerable<T> list, Func<T, TRet> selector)
{
    return list.Select(selector);
}

但我无法弄清楚如何使用默认方法扩展现有界面。

However I can't figure out how to use default methods to extend an existing interface.

此外，这显然是一个微不足道的例子。一般来说，我希望能够扩展列表< T> 和 Iterable< T> 接口与流api交互更容易。

Also, this is obviously a trivial example. In general, I would like to be able to extend the List<T> and Iterable<T> interfaces to make interacting with the streams api easier.

推荐答案

否;你不能这样做。

默认方法与扩展方法不同;它们只能在原始界面中定义。

Default methods are not the same as extension methods; they can only be defined within the original interface.

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