成员变量，必须扩展类A并实现某些接口 [英] Member variable which must extend class A and implement some interface

问题描述

我需要在一个类中有一个变量，该类是"ClassA"类的实例，但它也实现了"InterfaceI"接口.

I need to have a variable in a class which is an instance of class "ClassA" but which also implements interface "InterfaceI".

显然，这可以轻松地实现:

Obviously this can be done for one or the other easily:

private ClassA mVariable;
private InterfaceI mVaraible;

但是如何强制对象扩展ClassA和实现InterfaceB?像这样:

but how can I enforce the object both extends ClassA and implements InterfaceB? Something like:

private <? extends ClassA & InterfaceI> mVaraible;

是我所需要的，但我不了解语法，甚至不知道是否有可能.我还需要一个get and set方法，但是可以使用泛型(我认为吗?)

is what I need but I have no idea of the syntax or if it is even possible. I will also need a get and set method, but that can be done with generics (I think?)

显而易见的解决方案是

public class ClassB extends ClassA implements InterfaceI{
    //whatever here
}

尽管InterfaceI和ClassA都是外部库的一部分，但是该库具有扩展ClassA和InterfaceI的类，并且我无法对其进行编辑以使其扩展为ClassB，因此此解决方案将不起作用.

However both InterfaceI and ClassA are part of an external libary, this libary has classes which extend ClassA and InterfaceI and I cant edit them to make them extend ClassB, therefore this solution will not work.

推荐答案

我发现了一个相当棘手的解决方法.

I have found a rather hacky workaround.

该类同时包含ClassA和InterfaceI引用:

The class contains both a ClassA and InterfaceI reference as follows:

private ClassA mItemClassA;
private InterfaceI mItemInterfaceI;

set方法如下:

public void setVaraible(ClassA item){
    assert (item instanceof InterfaceI);
    mItemClassA = item;
    mItemInterfaceI = (InterfaceI) item;
}

如果项不是InterfaceI的实例，则此方法的其他变体可能会引发异常，返回false等.

Other variations of this could be throwing an exception, returning false, etc if the item is not an instance of InterfaceI

然后，该类中的其他方法可以使用mItemClassA和mItemInterfaceI从InterfaceI和ClassA调用函数.

Other methods in the class can then call functions from both InterfaceI and ClassA using mItemClassA and mItemInterfaceI.

我暂时不会实现get方法，但是如果我这样做了，那么可能必须有一个版本才能获取接口和一个版本才能获取类.

I am not going to implement a get method for now, but if I did there would likely have to be a version to get the interface and a version to get the class.

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