类型不匹配错误:无法从 ArrayList<SubClass1> 转换列出<SuperClass> [英] Type mismatch Error : Cannont convert from ArrayList&lt;SubClass1&gt; to List&lt;SuperClass&gt;

问题描述

这是我的班级结构，以及出现错误的地方

Here is my class Structure, and where I am getting error

class SuperClass{
//variables
}

class SubClass1 extends SuperClass{
//variables
}

class SubClass2 extends SuperClass{
//variables
}

class AClass{
List<SuperClass> list;

public AClass(boolean b){
if(b)
list = new ArrayList<SubClass1>();//getting error here
else
list = new ArrayList<SubClass2>();//and here
}
void addObjects(SuperClass obj){
list.add(obj);
}

}

我该如何解决这个问题?我应该改变我的设计吗?怎么样?

How can I solve this? Should I change my design ? How?

补充:

当我改变时

`List<SuperClass> list;`

到<代码>列表列表;

我没有收到上一个错误，但在添加对象时遇到另一个错误，

I am not getting the previous error but I am getting another error while adding objects,

类型 List不适用于参数(SuperClass)

推荐答案

您似乎正在尝试创建一个仅包含来自特定子类的对象的列表.在这种情况下，您只需要泛型在编译时表现良好.(泛型在运行时被删除:))

It seems you're trying to create a list that only contains objects from the particular subclass. In this case you just need the generics to play nice at compile time. (Generics are erased at runtime :) )

class AClass<T extends SuperClass> {
    List<T> list;

    public AClass(){
        list = new ArrayList<T>();
    }

    void addObjects(T obj){
        list.add(obj);
    }

}

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