为什么Arrays.asList（）返回了自己的ArrayList实现 [英] Why does Arrays.asList() return its own ArrayList implementation

问题描述

我最近发现，居然有在Java 2个不同的的ArrayList 实现（总好过从来没有我猜...）。

I recently found out that there are actually 2 different ArrayList implementations in Java (better late than never I guess...).

所以我想知道为什么 Arrays.asList（T ...一）需要返回不能被调整名单？如果他们需要一个不可修改的列表，为什么添加设置（INT指数，E元素）方法呢？

So I was wondering why does Arrays.asList(T... a) need to return a list which can not be resized ? If they needed an unmodifiable list why add the set(int index, E element) method then ?

所以，我一般的问题是，为什么不返回的java.util.ArrayList 从 Arrays.asList（T ...一）的方法？

So my general question is why not return the java.util.ArrayList from the Arrays.asList(T... a) method ?

另外你怎么用 java.util.Arrays.ArrayList 实施获得？

Also what do you gain with the java.util.Arrays.ArrayList implementation ?

推荐答案

您问：

另外你怎么用增益
  java.util.Arrays.ArrayList
  执行？

Also what do you gain with the java.util.Arrays.ArrayList implementation ?

这是因为通过Arrays.asList返回数组$ ArrayList是只是原来阵列上的看法。所以，当原始数组被改变，那么该视图过改变。

It is because the Arrays$ArrayList returned by Arrays.asList is just a view on the original array. So when the original array is changed then the view is changed too.

如果人会使用一个真正的ArrayList那么元素将被复制，并还原最初阵列上的变化不会影响，积极挖掘该ArrayList

If one would use an real ArrayList then the elements will be copied, and a change on the orignal array would not infuence the ArrayList.

的原因要做到这一点是非常简单的：

The reasons to do this are quite simple:

• 性能：无需复制点儿


• 内存efficent：不需要第二个数组

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