继承超类的ArrayList属性，但在子类中为其分配不同的类型 [英] Inheriting ArrayList property from superclass but assigning different types to it in child classes

问题描述

我有一个超类A，它有一个受保护的 ArrayList< Object> contentList 。我有从A继承的类B和C.

每个B和C在其构造函数中使用不同类型的ArrayList初始化contentList

  class B extends A 
 {
 public B（ArrayList< BContent> content）
 {
 contentList = content ; 
} 
 ... 
} 
 
 
 class C扩展了A 
 {
 public C（ArrayList< CContent> content ）
 {
 contentList = content; 
} 
 ... 
} 
  

BCOntent 和 CContent 和来自Object的数据结构子类。
$ b 编译器抱怨这是不被接受的，我必须将 contentList 的声明类型从 ArrayList< Object> 更改为 ArrayList< BCOntent> 或 ArrayList< CCOntent> $ b

我来自Objective-C背景，这可能是由于动态类型解析。如何在Java中实现此功能？

欢呼
AF

解决方案

您可以使用泛型。

  class A< T> {
受保护的列表< T>内容; 
} 
 
 class B extends A< BContent> {
 ... 
} 
  

这意味着 A 可以用于不同的可能类型（ T ）作为其内容。 A< BContent> 持有 BContent ，并且 A< CContent> 持有 CContent 。

I have a superclass A that has a protected ArrayList<Object> contentList. And I have classes B and C that inherit from A.

Each of B and C initialise contentList in their constructor with ArrayList of different types

class B extends A
{
    public B (ArrayList<BContent> content)
    {
        contentList = content;
    }
...
}


class C extends A
{
    public C (ArrayList<CContent> content)
    {
        contentList = content;
    }
...
}

Both BCOntent and CContent and data structure subclasses from Object.

The compiler is complaining that this is not accepted and that I have to change the declaration type of contentListfrom ArrayList<Object> to ArrayList<BCOntent> or ArrayList<CCOntent>

I come from Objective-C background and this is possible due to dynamic type resolution. How can I achieve this in Java?

Cheers AF

解决方案

You could use generics.

class A<T> {
    protected List<T> content;
}

class B extends A<BContent> {
    ...
}

This means that A can be used with different possible types (T) as its content. A<BContent> holds BContent, and A<CContent> holds CContent.

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