java&接口方法中的上界参数

我有一个包含映射函数的散列映射，它将X1类型的特定实例转换为X2类型的特定实例。X1的类对象用作此映射的键。示例代码：

public class Application {

    interface X1 {}
    static class A1 implements X1 {}
    static class B1 implements X1 {}

    interface X2 {}
    static class A2 implements X2 {}
    static class B2 implements X2 {}

    @FunctionalInterface
    interface Mapper<T extends X1> {
        X2 convert(T from);
    }

    public static void main(String[] args) {
        Map<Class<? extends X1>, Mapper<? extends X1>> map = new HashMap<>();

        map.put(A1.class, (A1 x1) -> /* some logic */ new A2());
        map.put(B1.class, (B1 x1) -> /* some logic */ new B2());

        X1 input = new A1();
        Mapper<? extends X1> mapperFunction = map.get(input.getClass());
        X2 output = mapperFunction.convert(input); // <- Required type: capture of ? extends X1, Provided: X1
    }
}

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是否可以修复所需的类型：捕获？扩展X1，前提是：X1错误而不将mapperFunction强制转换为Mapper？

我建议按以下方式更改代码，希望这有助于解决您的任务：

public class Application {

    interface X1 {}
    static class A1 implements X1 {}
    static class B1 implements X1 {}

    interface X2 {}
    static class A2 implements X2 {}
    static class B2 implements X2 {}

    @FunctionalInterface
    interface Mapper {
        X2 convert(X1 from);
    }

    public static void main(String[] args) {
        Map<Class<? extends X1>, Mapper> map = new HashMap<>();

        map.put(A1.class, (X1 x1) -> /* some logic */ new A2());
        map.put(B1.class, (X1 x1) -> /* some logic */ new B2());

        X1 input = new A1();
        Mapper mapperFunction = map.get(input.getClass());
        X2 output = mapperFunction.convert(input);
    }
}

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你必须投。要么在地图绘制程序中，要么在你得到它之后。