我怎样才能切一个ArrayList了在Java中ArrayList的？ [英] How can I slice an ArrayList out of an ArrayList in Java?

问题描述

我如何获得的ArrayList Java中的数组切片？具体来说，我想要做这样的事情：

How do I get an array slice of an ArrayList in Java? Specifically I want to do something like this:

ArrayList<Integer> inputA = input.subList(0, input.size()/2);
// where 'input' is a prepouplated ArrayList<Integer>

所以，我预计今年的工作，但Java的返回列表 - 所以它是不兼容的。当我尝试投它，Java将不会放过我的。我需要一个的ArrayList - ？我该怎么办

So I expected this to work, but Java returns a List - so it's incompatible. And when I try to cast it, Java won't let me. I need an ArrayList - what can I do?

推荐答案

在Java中，它使用的接口类型，而不是具体的类中的API很好的做法。

In Java, it is good practice to use interface types rather than concrete classes in APIs.

您的问题是，你正在使用的ArrayList （可能在很多地方），你真的应该使用列表。因此，您创建了自己的问题，造成不必要的限制，该清单是的ArrayList 。

Your problem is that you are using ArrayList (probably in lots of places) where you should really be using List. As a result you created problems for yourself with an unnecessary constraint that the list is an ArrayList.

这是您的code应该是什么样子：

This is what your code should look like:

List input = new ArrayList(...);

public void doSomething(List input) {
   List inputA = input.subList(0, input.size()/2);
   ...
}

this.doSomething(input);

---

您提出的解决方案，问题是/是这样的：

---

Your proposed "solution" to the problem was/is this:

new ArrayList(input.subList(0, input.size()/2))

这是通过使子表的副本的作品。它是不是在正常意义上的切片。此外，如果子列表大，则使得副本将是昂贵的。

That works by making a copy of the sublist. It is not a slice in the normal sense. Furthermore, if the sublist is big, then making the copy will be expensive.

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