为什么有人在java中使用Collections.emptyList？ [英] Why would someone use Collections.emptyList in java?

问题描述

可能重复：

Collections.emptyList（）vs. new instance

I尝试理解使用以下方式创建列表的新实例之间的区别：

I was trying to understand the difference between create a new instance of a list using:

new ArrayList<X>

和

Collections.emptyList();

根据我的理解，后者返回一个不可变的列表。这意味着不可能添加，删除或修改它。
我想知道为什么会创建和不可变的emptyList？有什么用？
感谢

As I understood, the later returns an immutable list. That means that it is not possible to add,delete, or modify it. I want to know why one would create and immutable emptyList ? what is the use? thanks

推荐答案

假设你必须返回一个集合而你不想创建几个对象时间。

Say you have to return a collection and you don't want to creating a couple of objects each time.

interface Configurable {
    List<String> getConfigurationList();
}

// class which doesn't have any configuration
class SimpleConfigurable implements Configurable {
    public List<String> getConfigurationList() { return Collections.emptyList(); }
}

返回空集合通常比返回 null

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