Java 与 base 和 child 相关的通用 class "not applicable for the arguments"

Question

我确实发现了关于一般问题的类似帖子，但没有一个以我能理解的方式解决了我的问题。我希望有人能帮我解决这个问题。

我尝试了很多方法，比如从不同的地方删除“?extends”并尝试使用“?super”来查看另一个错误是否会为我指明解决方案的方向。

以下代码：

final ResponseBase response = executor.execute(myRequest);

给我以下编译器错误： "The method execute(capture#6-of ? extends RequestBase) in the type CommandExecutor is not applicable for the arguments (RequestBase)"

完整代码清单：

public class MainClass {

    private final static Map<Class<? extends RequestBase>, CommandExecutor<? extends RequestBase, ? extends ResponseBase>> MAP = new HashMap<>();

    public static void main(String[] args) {

        final DummyCommandExecutor dummyCommandExecutor = new DummyCommandExecutor();
        MAP.put(MyRequest.class, dummyCommandExecutor);

        final RequestBase myRequest = new MyRequest();
        myRequest.setRequestString("this is my request");

        final CommandExecutor<? extends RequestBase, ? extends ResponseBase> executor = MAP.get(myRequest.getClass());

        final ResponseBase response = executor.execute(myRequest);

        System.out.println(response.getResponseString());
    }
}

interface CommandExecutor<T, R> {

    R execute(T object);

}

class DummyCommandExecutor implements CommandExecutor<MyRequest, MyResponse> {

    @Override
    public MyResponse execute(MyRequest request) {

        final MyResponse response = new MyResponse();
        response.setResponseString(request.getRequestString());

        return response;
    }

}

class MyResponse extends ResponseBase {

}

class ResponseBase {
    String responseString;

    public String getResponseString() {
        return this.responseString;
    }

    public void setResponseString(String responseString) {
        this.responseString = responseString;
    }
}

class MyRequest extends RequestBase {

}

class RequestBase {
    String requestString;

    public String getRequestString() {
        return this.requestString;
    }

    public void setRequestString(String requestString) {
        this.requestString = requestString;
    }

}

Answer 1

不进行转换就无法执行此操作。虽然您知道映射将 return 是给定类型的正确命令执行程序，但编译器不会，因此您需要告诉编译器不要关心：

final CommandExecutor<RequestBase,ResponseBase> executor = (CommandExecutor) MAP.get(myRequest.getClass());

Answer 2

你不能只匹配吗？与 T

一个选项就是做:

final CommandExecutor executor = MAP.get(myRequest.getClass());

如果地图 returns smth 不可施法

，当然可以在哪个选项中获得运行时间例外

Java 与 base 和 child 相关的通用 class "not applicable for the arguments"

Java Generic relating to base and child class "not applicable for the arguments"

java

generics

extends

wildcard