这两个java变量声明有什么区别？ [英] What's the difference between these two java variable declarations?

问题描述

public class SomeClass {
    private HashSet<SomeObject> contents = new HashSet<SomeObject>();
    private Set<SomeObject> contents2 = new HashSet<SomeObject>();
}

有什么区别？最后他们都是 HashSet 不是吗？第二个看起来对我来说是错的，但我已经看到它经常使用，接受和工作。

What's the difference? In the end they are both a HashSet isn't it? The second one looks just wrong to me, but I have seen it frequently used, accepted and working.

推荐答案

Set 是一个接口， HashSet 是一个实现 Set 接口的类。

Set is an interface, and HashSet is a class that implements the Set interface.

将变量声明为类型 HashSet 表示没有其他实现 Set 。如果您需要 HashSet 的特定功能，您可能需要这样做。

Declaring the variable as type HashSet means that no other implementation of Set may be used. You may want this if you need specific functionality of HashSet.

如果您不需要来自<的任何特定功能code> HashSet ，最好将变量声明为类型 Set 。这使得确切的实现可以在以后更改。您可能会发现，对于您正在使用的数据，不同的实现可以更好地工作。通过使用界面，您可以在以后需要时进行此更改。

If you do not need any specific functionality from HashSet, it is better to declare the variable as type Set. This leaves the exact implementation open to change later. You may find that for the data you are using, a different implementation works better. By using the interface, you can make this change later if needed.

您可以在此处查看更多详细信息：我什么时候应该在java中使用接口？

You can see more details here: When should I use an interface in java?

这篇关于这两个java变量声明有什么区别？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！