存储某些类JAVA的子类的哈希集合 [英] Hash set that stores subclasses of certain class JAVA

问题描述

考虑以下情况：

Consider the following situation:

public abstract class Vegetable {};

public class Tomato extends Vegetable {};
public class Cucumber extends Vegetable {};

public class Orange {};

关键是 - 我希望我的 HashSet 只存储延伸 Vegetable 的东西，我该怎么做？这应该很简单..

The point is - I want my HashSet to store only something extending Vegetable, how do I do this? This should be simple..

..但设置<？延伸蔬菜> （）hs = new HashSet <？延伸蔬菜> （）; 当然不是一个工作构造，Java希望我指定什么类型的 Set 我想要 - Tomato 或 Cucumber ，如果我只是想要蔬菜吗？

..but Set <? extends Vegetable> () hs = new HashSet <? extends Vegetable> (); is not a working construction of course, Java wants me to specify what type of Set I want - Tomato or Cucumber, what if I just want anything vegetable?

我宁愿不要使用任何强制转换...

I'd rather not to use any casts...

推荐答案

当您创建

When you create

Set<SomeType> = new HashSet<SomeType>();

该集合能够存储属于的任何子类的对象SomeType 。在你的情况下，你需要的只是

the set is capable of storing objects that belong to any subclass of SomeType. In your case, all you need is

Set<Vegetable> set = new HashSet<Vegetable>();

您现在可以这样做：

You can do this now:

set.add(new Tomato());
set.add(new Cucumber());

这样做会触发编译错误：

Doing this will trigger a compile error:

set.add(new Orange()); // Does not compile

就铸造而言，您不需要在其上投射对象进入集合。但是，如果您需要特定类型（即不是简单地 Vegetable ），则需要进行转换。

As far as casts go, you wouldn't need to cast objects on their way into the set. However, if you need a specific type (i.e. not simply Vegetable) on retrieval, you would need a cast.

这篇关于存储某些类JAVA的子类的哈希集合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！