forEach不修改java（8）集合 [英] forEach not modify java(8) collection

问题描述

假设我有一个整数列表，我在列表中使用Java 8 forEach方法将其值加倍。
说我有以下代码：

Say I have an Integer list and I'm using Java 8 forEach method on the list to double its values. Say I have the following code:

List<Integer> l = Arrays.asList(2,3,6,1,9);
l.forEach(p->p*=2);

至于每个方法取消费用并调用它接受方法。
我在运行上面的代码后打印列表，原始列表没有变化。

As forEach method take Consumer and calls it accept methos. I print the list after runnig the above code and the original list doesn't change.

据我所知，Stream不会改变源但是在这里我只是在每个元素上调用accept方法...

As far as I understand Stream doesn't alter the source but here I just call accept method on each element...

在advace中感谢你

Thank u in advace

推荐答案

forEach不改变列表的原因归结为规范：

The reason that forEach does not mutate the list comes down to the specification:

的forEach 说：

默认void forEach（Consumer<？super T> action）

.....默认实现的行为如下：

..... The default implementation behaves as if:

     for (T t : this)
         action.accept(t);

如您所见：

• 操作是消费者;即它不会生成值。


• 语义不允许更新此集合。

• The action is a Consumer; i.e. it doesn't generate a value.
• The semantics don't allow for the this collection to be updated.

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