Java多接口和反射 [英] Java multiple interfaces and reflection

问题描述

我有一个名为X的类，它实现了多个（例如3个）接口，称之为A，B和C.

I have a class called X that implements multiple (e.g. 3) interfaces, call them A, B and C.

我创建另一个扩展接口A的接口AB和B。

I create another interface AB that extends interface A and B.

如何使用反射创建可分配给接口AB的X实例？

How can I use reflection to create an instance of X that is assignable to interface AB?

我一直使用此代码获取ClassCast异常：

I keep getting ClassCast exceptions with this code:

package test.messages;

public interface A
{
    void methodA();
}

package test.messages;

public interface B
{
    void methodB();
}

package test.messages;

public interface C
{
    void methodC();
}

package test.messages;

public interface AB extends A, B
{

}

package test.messages;

public class X implements A, B, C
{
    @Override
    public void methodC()
    {
        System.out.println("C");
    }

    @Override
    public void methodB()
    {
        System.out.println("B");
    }

    @Override
    public void methodA()
    {
        System.out.println("A");
    }
}

然后在一个完全不同的类中：

Then in a completely different class:

AB api = (AB)Class.forName("test.messages.X").newInstance();

System.out.println(api);

现在当我尝试使用一个界面时，说A，它可以正常工作。

Now when I try with just one interface, say A, it works fine.

无论如何都可以使用组合界面AB吗？

Is there anyway to get it to work with the combined interface AB?

推荐答案

什么你真正想要的是 AND type - A& B 。 Java中通常不支持此操作。但是，我们可以创建一个包含类型A和类型B的包装类。（似乎每个问题都可以通过包装器解决：）

What you really want is AND type -- A&B. This is generally not supported in Java. However, we could create a wrapper class that contains a value that is both type A and type B. (It seems that every problem can be solved by a wrapper:)

public class AB<T extends A&B>
{
    public final T v;

    ... 
        v = (T)Class.forName("test.messages.X").newInstance();
}

而不是使用类型 A& B ，我们在需要的任何地方使用 AB<？> 。我们将在其 v 的字段上操作，这是 A 和 B 。

Instead of using type A&B, we use AB<?> everywhere it's needed. We'll operate on its field v, which is both A and B.

void foo(AB<?> ab)
{
    ab.v.methodOfA();
    ab.v.methodOfB();
}

或者你可以赚 AB A和B的子类型。

Or you could make AB a subtype of A and B too.

public class AB<T extends A&B> implements A, B
{
    public final T v;

    @Override // A
    public int methodOfA(){ return v.methodOfA(); }

在 https://stackoverflow.com/a/32659085/2158288

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